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INDIVIDUAL  DIFFERENCES  AND 

FAMILY  RESEMBLANCES  IN 

ANIMAL  BEHAVIOR 


A  STUDY  OF  HABIT  FORMATION 
IK    VARIOUS    STRAINS    OF   MICE 


BY 

HALSEY  J.  BAGG 


ARCHIVES  OF  PSYCHOLOGY 

BDITKD    BT 

R.  S.  WOODWORTH 
NO.   43,  JUNB,   192O 


Con   Mill  A    UWIVBHSITT  CONTBIBTTTION8  TO   PHILOSOPHr  AND   PSTCHOtOGT 

,  No.  4 


AGENTS:  G.  E.  STECHERT  &  CO.;  London  (^^fr  Yard.  Carey  9^W.  C.);  Leipzig  (Kbenigitr.,  37; 
Paris  (K 


THE  NEW  ERARPERS|NT)|NG  COMPANY 
LANCASTER,  PA. 


ACKNOWLEDGMENTS 

THE  writer  is  indebted,  above  all,  to  Professor  J.  McKeen  Cattell 
for  suggesting  the  problem,  and  for  helpful  criticism  and  encourage- 
ment throughout  the  experiment.  In  the  preparation  of  the  manu- 
script, and  in  the  evaluation  of  the  statistical  material,  thanks  are 
also  due  to  Professors  Robert  S.  Woodworth,  Edward  L.  Thorndike 
and  Henry  A.  Ruger. 


111 


CONTENTS 

I.     Historical    1 

II.     Statement  of  the  Problem 3 

III.  Methods  of  the  Experiment 4 

IV.  Tests  of  Learning  Ability 6 

(a)  In  the  Maze 6 

(&)  In  the  Multiple  Choice  Apparatus 6 

V.     Experimental  Results 9 

(a)  Time  and  Error  Averages  for  all  Tests 9 

(&)  Difference  in  Learning  between  Families  of  White 

and  Yellow  Mice 9 

(c)  Results  for  Maze  Test 11 

(1)  The  Initial  Learning 11 

(2)  The  Interference 17 

(3)  The  Retention  18 

(d)  Results  for  Multiple  Choice  Test 20 

VI.     Correlations  in  Learning  Records  between : 

(a)  Time  and  Error 23 

(&)  Performance  at  Beginning  and  End  of  Tests 24 

(c)  Initial  Learning  Records  and  Retention 24 

(d)  Performance  in  Maze  Test  with  Performance  in  Mul- 

tiple Choice  Test 26 

VII.    Family  Resemblances 26 

Mean  Variations  for  Related  and  Unrelated  Individuals . .  27 

VIII.     Sex  Differences  29 

(a)  Differences  in  Time  and  Error  Records 29 

(&)   Comparative  Distributions  of  the  Males  and  Females.  30 

(c )  Variability  of  the  Sexes 33 

IX.    Individual  Differences  and  Methods  of  Habit  Formation . .  35 

X.     Health  Conditions  and  Learning  Ability 42 

XI.     Family  Histories 44 

XII.     Summary  and  Results 


I.   HISTORICAL 

IN  the  present  thesis  an  effort  has  been  made  to  combine  in  a 
single  study  three  main  points  of  investigation;  first,  the  genetic 
study  of  behavior;  secondly,  the  subject  of  individual  differences; 
and  thirdly,  a  consideration  of  the  exact  method  of  habit  formation 
employed  by  the  mice  that  have  been  tested  in  the  experiments  that 
are  now  to  be  reported. 

Practically  no  experimental  work  has  been  done  upon  individual 
differences  and  family  resemblances  in  animal  behavior.  In  most 
cases,  the  behaviorist  has  been  content  to  study  the  mass  reaction  of 
a  group  of  animals  to  external  stimuli,  and  in  the  main,  has  not  at- 
tempted to  treat  the  variability  of  his  group  because  of  the  relatively 
small  number  of  animals  tested.  Professor  J.  McKeen  Cattell,  about 
fifteen  years  ago,  began  to  apply  the  methods  of  genetics  to  the  study 
of  conduct,  but  the  results  obtained  by  him  and  his  students  were 
not  published,  and  the  problem  has  been  given  to  me.  Yerkes  devotes 
a  chapter  of  his  book  on  "The  Dancing  Mouse,"1  to  differences  in 
behavior,  and  there  brings  together  results  for  variability  in  ".  .  . 
general  behavior,  rapidity  of  learning,  memory,  and  discrimination." 
His  results  showed  the  existence  of  a  considerable  amount  of  indi- 
vidual differences  in  the  behavior  of  the  dancing  mouse,  and  no 
family  resemblance  in  the  litters  he  obtained.  He  does  not  give 
quantitative  results,  but  confines  himself  to  a  general  discussion  of 
the  individual  peculiarities  of  the  animals  he  had  tested.  The  fol- 
lowing quotation  from  his  text  expresses  this  point:  "I  noted,  in  this 
test  of  the  animals '  ability  to  learn,  that  while  one  individual  would 
be  scurrying  about  trying  all  ways  of  escape,  investigating  its  sur- 
roundings, looking,  sniffing,  and  dancing  by  turns,  another  would 
devote  all  its  time  to  whirling,  circling,  or  washing  itself.  One  in 
the  course  of  its  activity  would  happen  upon  the  way  of  escape,  the 
other  by  reason  of  the  limited  scope  of  its  activity,  not  the  lack  of  it, 
would  fail  hour  after  hour  to  discover  even  the  simplest  way  of  get- 
ting back  to  its  nest,  to  food,  and  to  its  companions."  Concerning 
the  "inheritance  of  forms  of  behavior,"  Yerkes  found  that  certain 
lines  of  descent  exhibited  a  pronounced  tendency  to  whirl  to  the  left, 
while  others  reacted  in  the  opposite  direction.  When  two  such  strains 
were  crossed  the  offspring  showed  an  equal  frequency  of  left  and 

i  Yerkes,  Chapter  17,  "The  Dancing  Mouse." 
1 


2        INDIVIDUAL  DIFFERENCES  AND  FAMILY  EESEMBLANCES 

right  whirlers.  It  was  also  found  that  there  was  no  ' '  inheritance  of 
individually  acquired  forms  of  behavior."  Apparently  the  descend- 
ants of  animals  that  had  been  previously  trained  to  learn  a  certain 
task  were  given  no  advantage  over  ordinary  individuals  from  un- 
trained stock. 

G.  V.  Hamilton  in  his  monograph  entitled  ' '  A  Study  of  Persever- 
ance Reactions  in  Primates  and  Rodents,"2  found  that  there  were 
definite  types  of  behavior  exhibited  by  the  various  subjects  he  used. 
These  consisted  of  twenty  children,  a  baboon,  four  monkeys,  and  five 
kinds  of  rodents,  comprising,  one  mouse,  five  gray  rats,  five  black 
rats,  ten  white  rats  and  six  gophers.  The  reactions  of  the  monkeys 
and  the  baboon  presented  a  considerable  range  of  individual  differ- 
ences, which  determined  the  experimenter  in  the  selection  of  his  sub- 
jects, as  indicated  in  the  following  quotation :  ' '  The  marked  individual 
^differences  presented  by  the  five  infra-human  primate  subjects  reflect 
a  policy  of  selecting  subjects  in  whom  oddities  of  general  reactive 
equipment  had  been  observed."  Later  on  in  the  investigation  the 
author  refers  to  the  presence  of  individual  differences,  as  follows: 
"When  a  mammalian  is  confronted  by  a  series  of  situations  for  which 
he  is  unable  to  discover  and  stereotype  a  specifically  adequate  and 
invariably  successful  mode  of  response  he  tends  to  vary  his  response 
in  a  manner  which  is  less  a  species  than  an  individual  characteristic." 

The  writer  has  had  the  opportunity  of  going  over  the  original 
data  of  Basset's  work  on  white  rats,3  and  finds  that  a  certain  amount 
of  individual  difference  occurs  in  the  animals  he  tested.  Some  ani- 
mals did  consistently  better  work  than  others,  but  as  Basset  himself 
points  out,  his  numbers  were  too  few  to  make  possible  any  conclu- 
sions from  the  differences  that  were  observed. 

One  might  mention  a  large  number  of  isolated  cases  where  the 
literature  of  comparative  psychology  gives  evidence  of  individual 
differences.  It  would  not  be  worth  while  to  treat  them  here,  how- 
ever, because  they  generally  deal  with  relatively  few  animals,  and 
are  given  merely  as  side  issues  of  experiments  planned  to  bring  out 
other  factors. 

2  Hamilton,  "A  Study  of  Perseverence  Reactions  in  Primates  and  Rodents," 
Behavior  Monograph  Series,  No.  13,  1916. 

3  Basset,  "Habit  Formation  in  a  Strain  of  White  Rats  with  Less  than 
Normal  Brain  Weight,"  Behavior  Monograph  Series,  No.  9,  1914. 


II.    STATEMENT  OF  THE  PROBLEM 

THE  plan  of  the  experimental  work  presented  in  this  investiga- 
tion is  to  measure  individual  differences  in  behavior,  to  determine 
the  extent  to  which  the  animal  that  departs  from  the  average  in  one 
direction  will  depart  in  others,  to  measure  the  resemblances  in  fami- 
lies and  in  lines  of  descent,  and  to  determine  whether  kinds  of  con- 
duct can  be  established  in  family  lines  by  selection.  In  a  previous 
publication,4  of  which  this  thesis  is  a  continuation,  it  was  found  that 
individual  differences  occurred  in  the  ability  of  various  strains  of 
mice  to  learn  a  simple  maze,  and  also  that  a  family  resemblance 
existed  among  mice  of  the  same  litter,  that  amounted  to  a  coefficient 
of  correlation  in  the  neighborhood  of  0.50.  Certain  mice,  and  even 
whole  lines  of  descent,  showed  marked  variations  from  the  average, 
some  taking  more  than  twice  the  average  time  to  learn  a  given  task. 
These  differences  were  well  beyond  the  limits  of  the  probable  error. 
The  results  were  obtained  from  testing  90  mice,  as  determined  by 
the  time  required  to  find  their  way  through  a  maze.  Since  then, 
these  mice  and  their  offspring  have  been  tested  in  other  ways,  and 
further  experiments  are  now  in  progress  with  the  F7  and  F8  genera- 
tions. In  the  present  investigation  there  are  described  the  individual 
differences  and  family  resemblances  of  93  mice,  in  addition  to  the 
90  already  reported  on  in  the  previous  article.  These  mice  have 
been  tested  in  the  same  maze  as  were  the  previous  ones ;  in  addition, 
they  have  been  given  an  interference  test,  a  retention  test  and  have 
been  studied  in  a  second  maze,  as  described  below. 

*  Bagg,  ' '  Individual  Differences  and  Family  Resemblances  in  Animal  Be- 
havior," The  American  Naturalist,  April,  1916. 

The  present  material  was  submitted  for  publication  in  June,  1918. 


III.  METHODS  OF  THE  EXPERIMENT 

THE  first  maze  employed  was  designed  by  Professor  Cattell,  the 
plan  of  which  is  shown  in  Fig.  1.  The  animal  has,  in  the  first  com- 
partment, the  alternative  between  two  gates,  one  of  which  can  be 
pushed  open,  while  the  other  is  locked,  with  an  identical  situation 
in  a  second  compartment.  The  path  that  the  animal  must  follow 
can  be  altered  by  varying  the  position  of  the  open  gates.  "Unit 
construction"  is  used  in  the  dimensions,  which  are  adjusted  to  the 
size  of  the  animals  used,  and  which  permit  the  addition  of  any  de- 
sired number  of  standard  units. 

Preliminary  tests  were  made  with  albino  rats,  but  later  mice, 
which  are  more  active  and  more  easily  handled,  were  substituted. 
The  mice  were  given  one  trial  each  day  at  as  nearly  the  same  time  as 
possible.  Light  was  found  to  play  but  a  minor  role  in  the  tests,  day- 
light and  artificial  light  serving  equally  well.  At  the  outset  the  age 
of  the  mice  when  first  tested  was  not  always  known,  but  later,  when 
the  various  litters  were  obtained,  the  young  mice  were  tested  at,  or 
about,  the  age  of  four  weeks. 

The  mice  were  rewarded  for  a  successful  trial  by  a  mixed  diet  of 
milk,  bread,  oatmeal  and  sometimes  meat.  A  little  dry  bread  was 
always  in  their  cages.  Besides  satisfying  their  hunger,  the  mice  had 
the  additional  reward  of  a  place  to  exercise  and  the  companionship 
of  the  mice  that  had  just  been  tested.  The  order  of  the  tests  was 
varied  day  by  day.  In  case  the  way  through  the  maze  was  not  found 
in  360  seconds  the  animal  was  removed  and  tested  again  the  follow- 
ing day.  The  maximum  record  for  a  single  trial  is  360  seconds. 


METHODS  OF  THE  EXPEEIMENT 


IV.   TESTS  OF  LEARNING  ABILITY 

(a)  THE  MAZE  TEST 

IN  the  maze  test,  the  mice  were  first  given  an  initial  learning  test 
of  seventeen  trials.  This  was  a  desirable  number  for  two  reasons; 
first,  because  it  was  sufficient  for  the  average  mouse  to  learn  the  maze, 
and  secondly,  because  the  seventeen  trials  could  be  divided  into  three 
groups  representing  comparatively  distinct  stages  in  the  course  of 
learning.  The  first  stage  includes  the  first  two  trials  which  are 
largely  affected  by  chance,  and  although  given  here  for  complete- 
ness, are  not  averaged  in  the  final  ratings  for  each  individual.  The 
second  group,  including  the  next  five  trials,  represents  a  period  of 
continued  rapid,  but  less  variable  learning;  the  third  group,  includ- 
ing the  following  ten  trials,  covers  the  period  of  slow  or  nearly  com- 
pleted learning.  The  first  group  of  90  mice  was  given  only  this 
initial  learning  test  of  seventeen  trials.  The  behavior  of  the  latter 
group  of  93  mice  was  more  completely  studied.  After  the  seventeen 
trials  the  gates  were  changed,  so  that  the  ones  that  had  been  open 
were  locked,  and  those  closed  were  open.  This  was  an  interference 
test  designed  to  give  a  measure  of  the  adaptability  of  the  animals. 
It  was  necessary  for  the  mouse  to  break  the  old  habit,  and  learn  to 
get  through  the  maze  by  way  of  the  previously  closed  gates.  In  the 
first  trial  after  this  change,  the  interference  effects  were  pronounced, 
although  in  the  eleven  subsequent  trials  the  mice  rapidly  learned  the 
new  order.  The  interference  test  was  divided  into  two  groups.  The 
first  two  trials  were  put  in  one  group,  and  the  remaining  ten  trials 
in  a  second  group.  The  first  group  of  two  trials  gives  a  measure  of 
the  direct  effect  of  the  interference  upon  the  animal 's  behavior,  while 
the  second  group  of  ten  trials  shows  the  degree  to  which  this  inter- 
ference is  carried  over  into  the  following  trials,  and,  in  a  fashion, 
indicates  the  adaptability  of  each  animal  and  the  flexibility  of  its 
behavior. 

(b)  THE  MULTIPLE  CHOICE  TEST 

Upon  finishing  the  interference  tests  the  mice  were  immediately 
started  upon  a  second  experiment  which  will  be  here  called  the  mul- 
tiple choice  test.  A  plan  of  the  apparatus  is  given  in  Fig.  2.  The 
mouse  was  placed  in  the  maze,  through  the  door  marked  "E,"  within 
the  first  compartment.  Here  it  had  a  choice  of  one  of  four  gates, 


TESTS  OF  LEARNING  ABILITY 


marked  in  the  diagram  1,  2,  3,  4.  Three  of  these  gates  are  blue  and 
one  is  red.5  Punishment  was  given  at  the  blue  gates,  but  not  at  the 
red.  The  gates  are  the  same  size  as  those  used  in  the  maze  test  just 


5  The  Milton  Bradly  papers,  red  and  blue  were  used,  and,  in  so  far  as  the 
experiment  was  not  designed  to  test  the  color  sense  of  the  animals,  the  brightness 
value  of  the  colors  was  not  determined.  The  papers  were  changed  from  time  to 
time,  but  the  odor  factors  were  not  eliminated.  These  clews,  if  they  existed  as 
such,  for  the  animals,  were  purposely  retained,  and  the  mice  were  allowed  to 
make  use  of  them  in  solving  their  problems. 


8        INDIVIDUAL  DIFFEEENCES  AND  FAMILY  RESEMBLANCES 

described,  the  red  one  being  the  only  one  which  could  be  pushed 
open,  and  through  it  the  mouse  could  enter  the  second  compartment. 
If  the  mouse  attempted  to  pass  through  one  of  the  blue  doors  it  re- 
ceived a  slight  electric  shock  from  the  punishment  pad  "P,"  which 
was  on  the  floor  of  the  maze  directly  in  front  of  the  door.  The  posi- 
tion of  the  red  gate  was  changed  every  day,  being  now  in  one  place 
and  now  in  another,  following  a  program  which  had  previously  been 
made  out.  After  making  the  successful  choice,  the  mouse  entered 
the  second  compartment  where  he  was  free  to  go  directly  into  its 
nest  cage  by  means  of  one  of  the  exit  doors,  where  the  usual  reward 
was  given.  Twenty-five  trials  were  made  with  each  individual,  and, 
as  in  the  previous  maze,  the  trials  were  divided  into  three  somewhat 
homogeneous  groups.  The  first  group,  irregular  on  account  of  the 
great  play  of  chance,  includes  the  first  two  trials ;  the  second  group, 
including  the  next  five  trials,  marks  the  period  of  rapid  learning,  and 
the  third  group  of  eighteen  trials  represents  the  period  when  the 
learning  was  practically  completed.  It  has  been  found,  as  will  be 
discussed  later  on,  that  the  last  period  of  trials  was  longer  than 
necessary;  in  fact,  the  mice  showed  very  little  improvement  during 
this  period.  The  day  after  completing  the  trials  in  the  multiple 
choice  test  the  animals  were  given  a  series  of  trials  in  the  maze  test 
first  considered.  This  was  a  retention  test,  designed  to  give  a  measure 
of  the  permanence  of  association  for  the  previously  learned  task.  In 
this  case  ten  trials  were  given,  and  the  gates  were  opened  in  the  same 
order  as  during  the  last  ten  trials  of  the  interference  test. 


V.   EXPERIMENTAL  RESULTS 

(a)  TIME  AND  ERROR  AVERAGES  FOR  ALL  TESTS 

Tables  I.  to  VII.  give  the  time  and  the  number  of  errors,  i.e.,  the 
number  of  cases  in  which  the  mouse  tried  to  go  through  a  locked 
gate,  which  is  a  measure  of  the  activity  of  the  animal.  In  this  paper 
the  average  of  the  last  fifteen  trials  is  used  as  an  index  of  perform- 
ance for  the  first  set  of  seventeen  trials  in  the  maze  test,  and  the  last 
23  trials  are  used  as  an  index  for  the  25  trials  in  the  multiple  choice 
test,  in  each  case  the  first  two  trials  being  eliminated  for  irregulari- 
ties previously  mentioned.  The  groups  of  two  and  ten  trials  each  in 
the  interference  test,  and  the  group  of  ten  in  the  retention  test  are 
used  as  indexes  for  the  respective  cases.  The  above  tables  give  the 
complete  records  of  the  183  mice  tested,  grouped  in  families  as  de- 
scribed below.  The  average  time  is  54.12  ±  P.E.  2.3  seconds  per  trial 
for  the  last  fifteen  trials  in  the  maze  test;  60.26  ±  P.E.  4.7  seconds 
for  the  last  ten  trials  of  the  interference  test;  52.81  ±  P.E.  4.7  sec- 
onds for  the  retention  test,  and  39.47  ±  P.E.  .08  seconds  for  the  last 
23  trials  of  the  multiple  choice  test.  The  distributions  of  the  indi- 
viduals in  both  experiments  is  shown  in  Fig.  3.8  The  distribution 
for  the  animals  in  the  maze  test,  based  on  the  average  speed  attained 
in  the  last  fifteen  trials  is  indicated  by  the  solid  line,  and  the  distribu- 
tion for  those  in  the  multiple  choice  test,  based  on  the  speed  attained 
in  the  last  23  trials,  by  the  broken  line.  In  the  maze  test  65  animals 
took  less  than  20  seconds,  in  47  cases  the  time  was  between  20  and  40 
seconds,  and  there  were  71  cases  between  40  and  360  seconds.  But 
one  mouse  failed  to  learn  the  maze.  The  distribution  in  the  multiple 
choice  test  gave  30  cases  in  which  the  time  was  under  20  seconds,  20 
cases  between  20  and  40  seconds,  and  26  cases  between  40  and  280 
seconds.  None  of  the  mice  failed  to  learn  the  multiple  choice  test. 

(&)   DIFFERENCE  IN  LEARNING  BETWEEN  FAMILIES  OF  WHITE  AND 
YELLOW  MICE 

As  reported  in  the  preliminary  account  of  this  experiment,  it  was 
found  that  certain  strains  of  mice  took  considerably  longer  time  to 
learn  the  maze  than  others  tested  at  the  same  time.  Among  the 

"Seventy-six  of  the  183  cases  were  tested  in  both  the  mazes  given  in  these 
distributions. 


10      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

colored  mice  then  tested,  several  yellow  ones  made  poor  records. 
These  mice  were  mated,  and  they  and  their  offspring  compose  a 
group  of  27  individuals,  whose  average  time  and  error  record  is  con- 


o  SLO     60     100 


NuMber  05 

FIG.  3.     Total  Distribution  Curves  for  Maze  Test  and  Multiple  Choice  Test. 

siderably  poorer  than  the  normal  for  the  entire  population.7  The 
yellow  group  gave  an  average  time  of  83  ±  P.E.  7.0  seconds,  and  an 
average  of  2.0  errors  for  the  last  15  trials.  The  remaining  group  of 
63  mice,  mostly  white,  gave  an  average  time  of  27.5  ±  P.E.  2  seconds 
and  .9  error  per  trial.  The  yellow  mice  were  thus  found  to  take,  on 
the  average,  at  least  three  times  as  much  time,  and  to  make  twice  as 
many  errors  as  did  the  white  mice.  The  distribution  curves  for  the 
white  group  is  skewed,  most  of  the  individuals  falling  between  0  and 
20  seconds.  The  curve  for  the  yellow  family  is  nearly  flat,  there 
being  about  the  same  number  of  individuals  between  0  and  20  sec- 
onds, as  between  60  and  80  seconds,  and  between  140  and  160  seconds. 

7  This  group  of  27  mice  was  composed  (see  Tables  I,  IV  and  VII)  of  Nos. 
20  and  26,  and  their  seven  offspring;  No.  27,  the  sister  of  No.  26;  a  litter  of  five 
mice,  Nos.  32,  33,  34,  36  and  37  and  their  ten  offspring,  and  finally  two  unre- 
lated yellow  mice,  Nos.  2  and  3,  that  were  used  at  the  beginning  of  the  experi- 
ment. The  63  remaining  mice  of  the  white  group  bring  the  total  to  90. 


EXPERIMENTAL  RESULTS 


11 


TABLE  I 
COMPLETE  TIME  AND  ERROR  EECORDS  FOR  THE  YELLOW  FAMILY  IN  THE  MAZE  TEST 


No. 

First 
2 
Trials 

Next 
6 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

Error 
Aver- 
age 

No. 

First 
2 
Trials 

Next 
5 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

157 
64 
21 
12 
130 
77 
156 

Error 
Aver- 
age 

20  Y  9  ... 

360 

247 
234 
280 
182 
177 
360 
201 

41 
28 
43 
47 
136 

10 

58 
11 

14 
6 
8 

172 
14 

115 
21 

19 
19 

63 
183 
13 

1.6 
.2 
.4 
.5 
.9 
1.7 
3.7 
.5 

38Yc?.. 
39Yd"  

41Y  9 

360 
360 
360 

360 
357 
360 

277 
143 
47 

171 
130 
275 

98 

25 
9 
8 
109 
51 
98 

3.6 
2.3 

.8 
.5 
3.7 
2.4 
3.3 

21Wcf  

23  AGO*.  '.'.'..'. 
24AGd"  
25AaW  9  .... 
26Ytf  
27Y  9  

57Yc? 

58Y0" 

In  the  first  column  is  given  the  catalogue  number,  color  and  sex  of  the 
animals.  In  the  second  are  the  time  averages  (in  seconds)  for  the  first  two 
trials;  in  the  third,  for  the  next  five  trials;  in  the  fourth,  the  last  ten  trials,  and 
in  the  fifth  column  the  average  of  the  two  preceding  columns.  The  error  average 
for  the  last  15  trials  is  given  in  the  last  row  of  figures.  This  order  is  followed  in 
all  the  subsequent  tables,  but  in  Tables  III  and  VI  averages  are  added  for  the  last 
group  of  five  trials,  and  in  addition  these  tables  give  the  time  a»d  error  averages 
for  two  interference  tests  of  two  and  ten  trials  respectively;  a  retention  test  of 
ten  trials,  and  finally  the  averages  for  the  multiple  choice  test  of  23  trials,  which 
is  divided,  first,  into  a  group  of  the  two  first  trials,  next  the  following  five  trials, 
next  the  last  18  trials,  next  the  last  23  trials,  next  the  last  five  trials,  and  finally 
the  error  averages  for  the  last  23  trials. 

One  day's  record  has  been  omitted  for  mice  Nos.  27,  28,  29  and  31  because 
the  poor  records  for  that  day  were  obviously  due  to  a  constant  error,  on  account 
of  traveling,  etc.  These  are  the  only  cases  where  such  a  condition  has  occurred. 

(c)  RESULTS  FOB  THE  MAZE  TEST 

Fig.  4  gives  the  complete  record  curves  for  all  the  tests  given  in 
the  maze,  showing  curves  based  upon  the  average  and  the  median 
record  for  each  day,  and,  as  indicated  in  the  drawing,  these  may  be 
divided  into  three  main  parts:  first,  an  initial  learning  period  of 
seventeen  trials,  second,  the  interference  groups,  consisting  of  two 
and  ten  trials,  and  finally  a  retention  test  of  ten  trials.  183  mice 
were  tested  in  the  first  group  of  seventeen  trials,  and  71  in  each  of 
the  succeeding  groups.8  Two  daily  record  curves  were  calculated 
for  teach  test,  and  in  the  upper  curve  (represented  in  the  figure  by 
a  solid  line  and  marked  "average")  the  records  for  all  the  individ- 
uals in  each  group  were  averaged  for  each  successive  trial,  and  the 

8  The  tests  that  followed  the  initial  learning  period  of  seventeen  trials  were 
not  instigated  until  the  experiment  was  well  started  and  the  writer  had  become 
familiar  with  the  peculiarities  of  the  behavior  of  his  subjects.  Some  animals 
died  during  the  rather  long  period  in  which  they  were  observed,  and  their  incom- 
plete records,  although  given  in  the  tables,  are  not  averaged  in  Fig.  4. 


12      INDIVIDUAL  DIFFERENCES  AND  FAMILY  EESEMBLANCES 


probable  error  calculated  for  each  point  in  the  curve.  In  accord- 
ance with  a  plan  proposed  by  Professor  Cattell,  the  limits  of  the 
probable  error  are  shown  by  the  broken  lines.  The  chances  are  even 
that  with  a  greatly  increased  number  of  cases  the  time  would  have 
remained  between  these  limits,  and  a  nearly  smooth  curve  can  be 
drawn  within  them.  When  the  gates  were  changed  at  the  eighteenth 

TABLE  II 
COMPLETE  EECOEDS  FOE  THE  WHITE  FAMILY  IN  THE  MAZE  TEST 


No. 

First 
2 
Trials 

Next 
5 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

Error 
Aver- 
age 

No. 

First 
2 
Trials 

Next 
5 
Trials 

Last 
10 
Trials 

Last 
15 

Trials 

Error 
Aver- 
age 

12WO" 

360 
100 
316 
156 
185 
246 
56 
169 
196 
285 
360 
360 
222 
317 
360 
149 
360 
89 
84 
58 
86 
110 
252 

91 
159 
26 
16 
75 
25 
13 
12 
77 
87 
306 
173 
58 
162 
186 
121 
304 
29 
19 
16 
14 
16 
47 

56 
37 
17 
7 
25 
18 
7 
10 
34 
8 
17 
25 
17 
20 
91 
18 
30 
21 
13 
14 
7 
10 
33 

67 
91 
21 
10 
42 
20 
9 
11 
48 
35 
113 
75 
31 
68 
122 
53 
121 
24 
15 
15 
9 
12 
38 

1.9 
1.4 
.4 
.5 
1.9 
.7 
.5 
.9 
1.7 
.9 
1.2 
1.7 
.9 
1.0 
2.9 
.9 
1.7 
1.2 
1.2 
1.2 
.8 
.9 
1.6 

103Wcf... 
104Wd"  
105W  9  
106W9 

108 
174 

99 
284 
101 
93 
67 
151 
88 
75 
70 
183 
318 
81 
115 
118 
64 
76 
66 
25 
189 
90 
72 

5 
12 
12 
22 
69 
11 
13 
33 
11 
13 
13 
13 
11 
14 
40 
19 
17 
84 
39 
23 
15 
19 
22 

10 
13 
11 
12 
8 
7 
12 
8 
7 
5 
11 
8 
4 
10 
9 
7 
9 
7 
29 
10 
7 
9 
11 

8 
12 
11 
15 
28 
8 
12 
16 
8 
8 
12 
10 
7 
12 
20 
11 
12 
33 
32 
14 
9 
12 
15 

.5 
1.0 
.8 
.9 
.9 
.4 
1.0 
.9 
.7 
.4 
1.0 
.7 
.5 
1.0 
1.1 
.5 
.7 
.7 
2.2 
.9 
.5 
1.0 
.9 

13W9 

15W  9  

48W0" 

49W9 

109Wd" 

50W9 

HOWc? 

51W9 

lllWc? 

52W9 

mwc?1  

113Wc" 

53W9 

65W9 

114W  9  
115W  9  

newd"  

117WC?  
HSWd*  
119Wcf  
120W  9  
121W  9  
122Wc?  
123W  9  
124W  9  
125WC?  
126Wc?  
127W  9  

66Wc?  
67W  9  .  . 
76W9 

77Wc? 

78Wcf 

71Wd" 

72W9 

74W  9  
86W  9  
87W  9  
88W9 

89W  9  
91Wd"  

trial,  an  interference  effect  occurred  that  resulted  in  a  rise  of  the 
time  curve  to  118  seconds  at  the  first  trial.  This  was  just  half  the 
number  of  seconds  it  took  the  average  mouse  to  go  through  the  maze 
for  the  first  time.  The  rest  of  the  interference  test  showed  an  aver- 
age time  curve  that  was  above  the  curve  for  the  last  few  trials  of 
the  initial  learning  test,  except  for  the  sixth  day  of  the  interference 
test  when  the  curve  dropped  to  40  seconds.  The  curve  based  on  the 
average  for  the  interference  test  began  to  follow  the  usual  course  of 
learning  until  the  sixth  day  when  the  maximum  speed  record  was 
reached,  but  at  that  point,  for  some  unknown  reason,  a  retarding 
factor  occurred  that  caused  a  decided  rise  in  the  curve  from  then  to 
the  end  of  the  test.  There  are  two  possible  explanations  for  this 
phenomenon;  first,  that  at  the  lowest  point  of  the  curve  the  mice 
had  reached  their  maximum  speed  and  efficiency  and  thereafter  they 


EXPERIMENTAL  RESULTS 


'153 

i|lg 


si 


ii  I 


1 


II 


ill 


M       5 


ii 

EH 


INOSINOOOiOOOTHCOiO-HOlO^r-iOS-^^Hin 
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T^(Nt^CO»ClOOS?OO5t^iOt^«O'*N.O«5'*HCOt^O>O'-H—lt^>C 

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l-H  i-H  <N  1-1  T-H  r4  (N  IN*  r-J  ^-4  l-H  CO  CO*  Tji  l-H       "  N  1-H       '  •*'  CO  <N  CO       '  N  N  F-5 


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14 


INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

CicON          CO  rH  CO  CO          rHrHCOCOlHlNtNINrHC^TfrHCOlOCOrHCqlNCO 


rHIOO        lOrHO'*        M*  CO  CO  10  f-  CO  CO  O  <N  ^  b-  •<*  —I  00  OS  CO  <N  CO  IO 


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IrHCO          (MI>COCO 
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s 

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J  g  H  ti          COlOiO-^OOrHrHCJKNCOTiHI 

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5  5  «  CO          CO          CO  rH  rHrHIM  (N  rH  rH  rH 

i||ji         -*          <M 

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CN          rH          CO 

«-g  o2^SScO^^CO^r^MCNl(N^2Cy5""eON'^r^^e^2' 

OOO^COCDrHOrHlO>OO3CDOOOrHT}<O5CDt^COTt<rHrH(NCOrHTtHlO 
^  ,_,  rH  Tf<  CO  (N  CO  rH  rH  00          rH  (M  rH  O  00  (N          <N  rH  rH  rH  t^  rH  IO  CO  CNJ  Tt< 

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CH-<>^OF^^^Of^^^^^^OHC^c>rbrb'bfbOf(>'b<>rbfblb 

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iii 


EXPERIMENTAL  RESULTS 


15 


sift 

B5jH 


I! 


I! 


•*  (N  Cl  (N  CO  (N  CO  <N  (N 


I! 


CO  Tji  Tji  IN'  <N  >-H  <N  (N 


ooo'b'boi-ooo 


16      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

became  ' '  tired ' '  of  the  problem  and  lost  their  adjustment,  or  in  other 
words,  the  test  had  been  carried  too  long;  secondly,  the  following 
explanation  may  be  given:  the  drop  in  the  sixth  day  of  the  test  is 


not  significant  and  represents  a  chance  irregularity  which  would  dis- 
appear from  the  curve  if  a  still  greater  number  of  animals  was  used. 
As  there  is  no  evidence  to  support  the  first  of  these  explanations,  it 


EXPERIMENTAL  RESULTS 


17 


is  probable  that  the  second  solution  is  the  correct  one.  We  can,  there- 
fore, say  that  the  interference  as  shown  in  this  experiment  was  not  a 
transitory  thing,  being  evident  for  only  one  or  two  trials  after  its 
application,  but  instead,  it  exerted  an  influence  over  a  number  of 
trials  and  prevented  the  animals  from  attaining  the  same  degree  of 
proficiency  that  they  had  previously  shown  in  a  similar  task.  How- 
ever, if  the  interference  test  had  been  continued  it  is  possible  that 
the  curve  would  have  reached  as  low  a  record  as  that  given  by  the 
initial  learning  test. 

TABLE  IV 

COMPLETE  RECORDS  OF  A  FAMILY  CONSISTING  MOSTLY  OF  YELLOW  INDIVIDUALS 
IN  THE  MAZE  TEST 


No. 

First 
2 
Trials 

Next 
6 
Trials 

Last 
10 

Trials 

Last 
15 
Trials 

Error 
Aver- 
age 

No. 

First 
2 
Trials 

Next 
5 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

Error 
Aver- 
age 

1.0 
1.5 
1.2 
2.3 
2.0 
.7 
2.3 

32Yd*... 
33Yd*  
34Ycf  
36Yc?  
37Y  9  
54W9 

225 
154 
186 
354 
137 
360 
360 
360 

109 

186 
88 
55 
20 
36 
242 
130 

71 
42 
39 
28 
16 
34 
103 
103 

83 
90 

56 
37 
17 
35 
150 
112 

1.7 
.5 
1.0 
.9 
1.2 
.7 
3.5 
2.0 

eichd*  

62YWcf.... 
63  YW  9  .... 
64Y  9  
68YW  9  .... 
69Ycf  
70Y  9  

360 

312 
243 
360 
112 
177 
234 

202 
90 
130 
182 
71 
41 
223 

30 
18 
38 
113 
65 
9 
75 

87 

42 
69 
136 
67 
19 
124 

55Yc?  

56Y9 

TABLE  V 

COMPLETE  RECORDS  OF  A  SMALL  FAMILY  SHOWING  GOOD  RECORDS  IN  THE  MAZE 

TEST 


No. 

First 
2 
Trials 

Next 
5 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

Error 
Aver- 
age 

No. 

First 
2 
Trials 

Next 
6 
Trials 

Last 
10 
Trials 

Last 
15 
Trials 

8 

6 

31 

Error 
Aver- 
age 

29W  9  .  . 
30GR01... 
44W  9  

229 

58 
297 

9 
43 
16 

8 
33 

7 

8 
36 
10 

1.3 
1.0 
.5 

45W  9  
46GRcf  
47816"  

142 
141 
150 

13 
9 

34 

5 
4 
29 

.5 

.5 
1.0 

It  is  interesting  to  note  that  Hunter  and  Yarbrough  found  that 
interference  occurred  between  an  old  habit  and  the  formation  of  a 
new  one,  in  their  study  of  the  auditory  habits  in  the  white  rat.9  The 
following  is  quoted  from  their  results:  "Habit  interference  occurs 
in  the  white  rat  between  a  first  habit  and  the  formation  of  the  second 
one."  "Interference  is  most  marked  between  the  end  of  the  per- 
fected habit  and  the  beginning  of  the  new  habit."  "Habit  inter- 
ference may  serve  greatly  to  slow  up  the  formation  of  a  new  habit. ' ' 
The  results  of  this  investigation  agree,  in  the  main,  with  the  state- 
ments that  have  just  been  quoted,  but,  although  the  interference 
effect  caused  a  sharp  rise  in  the  time  curve,  and  the  interference  was 

9  Walter  S.  Hunter  and  Jas.  N.  Yarbrough,  ' '  The  Interference  of  Auditory 
Habits  in  the  White  Rat,"  The  Journal  of  Animal  Behavior,  Vol.  7,  No.  1. 


18      INDIVIDUAL  DIFFERENCES  AND  FAMILY  EESEMBLANCES 

evident  throughout  the  subsequent  trials,  yet  it  did  not  appear  to 
slow  up  the  formation  of  a  new  habit  to  as  great  a  degree  as  might 
be  expected  from  the  nature  of  the  behavior  that  was  tested.  The 
quick  recovery  from  the  interference  effect  suggests  that  the  be- 
havior of  the  animals  of  this  investigation  shows  a  considerable 
amount  of  flexibility.  As  was  previously  stated,  the  animals  took 
only  half  as  much  time  to  go  through  the  maze  on  the  day  when  the 
interference  was  given  as  they  did  on  the  first  day  they  were  tested, 
and  this  shows  that  an  accelerating  transfer  effect  from  the  previous 
training  was  operating  to  counteract  the  slowing  up  of  the  inter- 
ference. 

In  order  to  more  carefully  analyze  the  behavior  of  the  mice  the 
median  record  was  calculated  for  each  day's  performance,  and  a 
curve  based  upon  the  same  is  represented  by  the  dotted  lines  in  Fig. 
4.  It  may  be  noted  that  for  each  test  the  curve  based  on  the  median 
falls  considerably  below  the  corresponding  curve  for  the  average. 
The  essential  character  of  the  curves,  found  by  these  different  meth- 
ods, is  the  same;  except  that  the  curve  based  upon  the  median  is 
more  regular  than  the  one  found  from  the  average.  In  the  inter- 
ference test  the  curve  for  the  median  records  is  much  more  regular 
than  that  of  the  average  curve  for  the  same  test,  while  no  disturb- 
ance at  all  is  to  be  noted  at  the  sixth  day  of  that  test.  The  character 
of  the  curve  based  on  the  median  supports  what  has  already  been 
said  concerning  the  permanence  of  the  interference  effects  over  a 
number  of  trials. 

The  retention  test  shown  in  Fig.  4  was  given  immediately  after 
the  mice  had  been  tested  in  the  multiple  choice  test,  and  may  repre- 
sent a  certain  amount  of  training  acquired  there.  The  average  time 
for  the  last  ten  trials  of  the  interference  test  is  60.26  ±  P.E.  4.7, 
while  the  average  time  for  the  ten  trials  in  the  retention  test  is  52.81 
±  P.E.  4.7.  The  superiority  of  the  average  retention  test  in  time  is 
nearly  twice  its  P.E.,  indicating  a  fair  reliability.  The  superiority 
of  the  retention  test  may  be  due  to  the  presence  of  one  or  more  of 
the  following  conditions:  (1)  A  mere  carrying  over  of  capacity  at- 
tained in  the  interference  test.  (2)  The  dying  out  of  bonds  devel- 
oped in  the  negative  test  (which  in  this  case  was  the  initial  learning 
test),  and  the  strengthening  of  bonds  developed  in  the  interference 
test.  (3)  The  transfer  of  capacity  developed  in  the  multiple  choice 
test.  Now  1  is  not  likely  because  the  average  record  made  in  the 
retention  test  was  much  better  than  that  in  the  interference  test 
even  after  a  considerable  interval  of  time.  It  is  possible  that  the 
condition  in  2  may  account  for  the  facts,  but  there  is  no  direct  con- 


EXPERIMENTAL  EESULTS 


19 


>        fl 


S 


il 


111 


III 


i 


t^OOt 


".-H      'rH(N'**C<3(N'-i      'COO 


rH^H(N  ,-H          <N<N(M' 


Tt<OCO05i-lT^(McOeO'-i'-<O<NO5COOfO—  ICO 

»-l          IO  T-H          i-H  t^  >O  I»~l  i-H  >-H  i-H 


'w^oo'0'0'*00'*^^^^ 


•    •oo'b'b'b'booo   • 
o'bowoooooo  B*" 


20      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 


firmatory  evidence  from  the  data,  and  it  must  be  remembered  that 
the  original  test,  although  older  than  the  interference  test,  still  re- 
ceived a  greater  amount  of  repetition.  It  appears  from  the  results 
of  the  experiment  that  the  condition  in  3  is  most  likely  to  account  for 

TABLE  VII 
COMPLETE  EECORDS  OF  THE  UNRELATED  INDIVIDUALS  IN  THE  MAZE  TEST 


First 

Next 

Last 

Last 

Error 

First 

Next 

Last 

Last 

Error 

No. 

2 

5 

10 

15 

Aver- 

No. 

2 

5 

10 

15 

Aver- 

Trials 

Trials 

Trials 

Trials 

age 

Trials 

Trials 

Trials 

Trials 

age 

IChcf  

212 

48 

11 

23 

1.0 

5W9-. 

74 

22 

8 

12 

.6 

2Y9 

285 

213 

103 

140 

5  1 

28Wcf 

W1 

38 

5 

17 

1  0 

3Y9 

316 

55 

63 

61 

3  3 

31GB  9 

130 

78 

15 

38 

1  0 

4Wo" 

77 

18 

14 

16 

7 

SSWd1 

131 

14 

q 

11 

8 

90Ch  9  

202 

81 

13 

35 

1.0 

the  facts;  that  is,  the  transfer  of  capacity  developed  in  the  multiple 
choice  test  accounted  for  the  superiority  of  the  retention  test,  by 
virtue  of  the  better  adjustment  that  the  animals  received  to  the  ex- 
periment as  a  whole,  and  by  practise  in  the  elimination  of  fruitless 
movements.  The  number  of  seconds  required  for  the  average  mouse 
to  complete  the  first  trial  of  the  retention  test  is  below  all  but  one  of 
the  records  that  the  same  mice  made  in  the  interference  test,  and  it 
is  noteworthy  that  the  curve  for  the  retention  test  based  on  the  daily 
average,  is  not  similar  to  either  of  the  preceding  curves,  but  is  nearly 
flat,  except  for  a  slight  rise  at  the  last  trial.  Since  the  average 
animal  did  not  start  with  a  high  time  record,  it  is  evident  that  it  did 
not  need  to  learn  the  task  all  over  again,  but  showed  a  considerable 
amount  of  permanence  of  association  for  the  previously  learned  task. 
The  curve  for  the  retention  test,  based  on  the  median  record  for 
each  day,  confirms,  in  the  main,  what  has  already  been  said  concern- 
ing this  test.  The  curve  for  the  median  is  also  flat,  the  four  high 
points  all  reaching  to  about  a  score  of  twenty  seconds,  and  it  again 
shows  the  relative  superiority  in  the  record  for  the  first  day  of  the 
test.  Also,  taken  day  by  day,  the  records  for  the  retention  test,  with 
a  single  exception,  show  the  retent;on  test  with  daily  records  su- 
perior to  the  corresponding  ones  of  the  interference  test. 

(d)  RESULTS  FOR  MULTIPLE  CHOICE  TEST 

Fig.  5  gives  complete  record  curves  for  the  same  71  mice  as  tested 
by  the  multiple  choice,  and  the  limits  of  the  probable  error,  for  the 
curve  based  on  the  daily  average,  are  indicated  in  the  same  manner 
as  explained  for  the  previous  curves.  The  average  time  for  the  first 
trial  in  the  maze  test  is  236  seconds  as  compared  with  91  seconds  as 


EXPERIMENTAL  RESULTS 


21 


the  average  for  the  first  trial  of  the  multiple  choice  test.  How  much 
this  difference  is  due  to  what  the  average  animal  acquired  in  the 
first  experiment  can  not  be  determined  since  the  tests  themselves  are 
markedly  different.10  In  the  first  place,  the  distance  to  be  traversed 

•  00- 


80. 
60 


ao 


\ 


/  J-  /O  /5  AO  2.5 

Number  oj  TriA)& 

FIG.  5.  Complete  Eecord  Curves  for  Mice  in  the  Multiple  Choice  Test, 
showing  curves  based  upon  the  average  and  the  median  for  each  day.  (The 
limits  of  the  probable  error  for  the  average  curve  are  indicated  by  the  broken 
lines.) 

in  the  multiple  choice  test  is  much  shorter  than  in  the  maze  test,  and 
the  intensity  of  punishment  is  greater  in  the  former  case  because 
there  the  electric  shock  was  used.  Also  color  clews,  and  the  fact  that 
it  was  necessary  for  the  animal  to  go  through  only  one  door,  tend 
to  lessen  the  average  time  in  the  multiple  choice  test.  As  indicated 
in  the  previous  discussion,  there  was  no  doubt  a  transfer  effect  in 
learning  from  the  first  task  to  the  second,  that  would  again  result 
in  shortening  the  time  in  the  multiple  choice  test.  This  was  due; 
first,  to  a  better  general  adaptation  to  the  experiment  as  a  whole, 
which  was  carried  over  from  the  maze  test ;  and  secondly,  to  the  fact 
that  an  important  element  was  common  to  both  tasks,  namely,  that 
in  each  case  the  animal  learned  to  escape  from  confinement  by  means 
of  a  door  that  could  be  pushed  open.  It  is  interesting  to  note  at  this 
point  that  Yerkes  in  his  study  of  the  dancing  mouse1  (see  page  263) 
found  that  experience  in  one  labyrinth  made  the  learning  in  a  second 
labyrinth  much  easier.  "Those  individuals  whose  first  labyrinth 
training  was  in  (labyrinth)  C  made  their  first  correct  trip  as  the 
result  of  19.7  trials,  whereas  those  which  had  previously  been  trained 
in  labyrinth  B  were  able  to  make  a  correct  trip  as  the  result  of  only 
7.0  trials.  Similarly  the  table  shows  that  training  in  C  rendered  the 
10  This  point  is  being  more  closely  studied  in  an  experiment,  now  under  way. 


22      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

subsequent  learning  in  B  easier. ' '  The  average  curve  in  Fig.  5  indi- 
cates that  there  is  practically  no  increase  in  learning  between  the 
seventh  trial  and  the  twenty-fifth.  A  fairly  uniform  decrease  in 
time  occurs  from  the  first  to  the  seventh  day,  when  an  average  speed 
of  twenty-six  seconds  was  made.  The  only  other  performance  that 
bettered  this  record  was  made  on  the  twenty-fourth  day,  when  an 
average  time  of  twenty- four  seconds  was  recorded.  The  number  of 
trials  in  the  multiple  choice  test  could  have  been  much  less  and  still 
sufficient  for  the  average  mouse  to  learn  the  maze.  It  was  impossible 
to  determine  that  more  trials  were  given  than  were  necessary  until 
the  experiment  was  well  started.  In  fact,  the  experimenter  arbi- 
trarily chose  twenty-five  as  the  number  of  trials  because  he  thought 
it  would  take  the  average  mouse  longer  to  learn  the  second  task  than 
the  first.  As  explained  above,  the  results  of  the  experiments  dis- 
approved this  assumption. 

In  the  multiple  choice  test,  the  curve  based  on  the  median  record 
for  each  day,  as  in  the  previous  tests,  is  considerably  below  the  cor- 
responding curve  for  the  average.  The  curves  here  are  essentially 
similar,  and  it  may  be  noted  that  the  curve  for  the  median,  after  the 
second  trial,  never  rises  higher  than  twenty  seconds  or  lower  than  ten. 


VI.    CORRELATIONS  IN  LEARNING  RECORDS 


VARIOUS  correlations  have  been  calculated  for  performance  in  one 
task  with  performance  in  another,  and  between  groups  of  trials 
within  a  single  task.  The  correlation  have  all  been  positive,  varying 
from  0.11  to  0.85  as  described  below.  A  complete  list  of  the  correla- 
tions is  given  in  Table  VIII.  The  Pearson  formula, 

TABLE  VIII 
KESUI/TS  OF  CORRELATIONS 


No. 

Things  Correlated 

Correlations 

1. 

2. 

Time  in  last  15  trials  of  maze  test  with  error  average  in  same  task 
Time  in  first  group  of  5  trials  in  maze  test  with  the  time  in  last 
group  of  5  trials  in  maze  test  

+0.85 

+0.46 

3. 

4. 

5. 

Time  in  last  15  trials  of  maze  test  with  the  time  in  retention  test  . 
Time  in  last  15  trials  of  maze  test  with  the  time  in  the  first  2 
trials  of  the  interference  test  
Time  in  last  15  trials  of  maze  test  with  the  time  in  the  last  10 
trials  of  the  interference  test      

+0.35 
+0.55 
+0.49 

6. 

Time  in  last  23  trials  of  Multiple  Choice  test  with  error  average 
made  in  same  test                               

+0.82 

7. 
8. 

Time  in  first  group  of  5  trials  in  Multiple  Choice  test  with  the 
time  in  last  group  of  5  trials  in  Multiple  Choice  test  
Time  in  last  group  of  15  trials  in  maze  test  with  the  time  in  last 
group  of  23  trials  in  Multiple  Choice  test  

+0.25 
+0.11 

2(*  '  0) 

Vsz2-  Vs*/2' 

was  used  for  the  correlations  numbered  in  the  table  as  1,  2,  6  and  7. 
Because  the  remaining  correlations,  3,  4,  5  and  8  were  made  between 
two  groups  both  from  asymmetrical  distributions,  the  ranking  method 
was  used  with  the  following  formula: 


r  =  1  - 


6SD2 
n(n2  - 


The  ranking  method  was  employed  so  that  undue  weight  would  not 
be  given  to  the  few  extreme  cases  in  the  skewed  distributions.  This 
disadvantage  did  not  occur  in  the  correlations  made,  between  time 
and  error,  and  performance  at  the  beginning  and  end  of  the  tests, 
so  in  these  cases  the  Pearson  formula  was  used. 

The  correlation  between  the  time  in  the  initial  learning  period 
in  the  maze  test  with  the  errors  made  during  that  performance 

23 


24      INDIVIDUAL  DIFFERENCES  AND  FAMILY  SE 'SEMBLANCES 

amounted  to  -f-  0.85.  A  similar  coefficient  of  correlation  of  -f-  0.82 
was  found  to  hold  between  the  last  23  trials  of  the  multiple  choice 
test  and  the  errors  made  in  that  task.  These  results  are  what  one 
might  naturally  expect  to  find,  namely,  that  the  animal  that  made 
many  errors  required  more  time.  The  conclusion  need  not  hold, 
however,  for  the  type  of  behavior  that  this  investigation  deals  with, 
because  it  might  very  well  be  that  a  stupid  animal  was  one  likely  to 
sit  in  a  corner  of  the  maze  and  make  a  poor  time  record,  but  a  good 
error  record.  These  two  high  correlations  are  thus  seen  to  give  a 
measure  of  the  activity  of  the  animals  in  each  task,  and  they  show 
the  value  of  the  tests  that  were  used,  in  that  each  was  adapted  to 
the  instinctive  behavior  of  the  animals  tested.11  The  native  equip- 
ment of  the  mice  no  doubt  adapted  them  to  finding  their  way  through 
narrow  passages  and  forcing  their  bodies  through  small  openings. 

A  low  positive  correlation  of  0.11  was  found  to  hold  for  the  rela- 
tion between  the  initial  learning  period  in  the  maze  test  and  the  last 
23  trials  in  the  multiple  choice  test.  As  previously  discussed,  the 
time  values  in  the  two  tasks  that  were  correlated  are  not  comparable, 
and  this  fact  may  account  for  the  lowness  of  the  coefficient  of  corre- 
lation. 

A  correlation  was  made  between  performance  at  the  beginning 
and  close  of  the  trials,  and  in  this  case  the  first  group  of  five  trials 
was  correlated  with  the  last  group  of  five.  For  the  maze  test  this 
correlation  amounted  to  +0.46,  which  represented  a  fairly  strong 
correlation.  A  similar  correlation  between  the  first  group  of  five 
trials  and  the  last  group  of  five  trials  in  the  multiple  choice  test  gave 
a  lower  correlation  of  -(-0.25. 

The  correlation  between  the  initial  learning  period  in  the  maze 
test  and  the  retention  test  for  the  same  task  was  found  to  be  -f-  0.35. 
This  indicated  a  fairly  close  relation  between  proficiency  in  a  given 
task  and  the  amount  of  association  retained.  A  similar  correlation 
between  the  same  initial  learning  period  in  the  maze  test  and  the  first 

11  Guinea  pigs  have  been  used  as  subjects  of  another  investigation  and 
when  tested  in  the  maze,  that  apparatus  was  found  to  be  very  well  suited  to  their 
instinctive  type  of  behavior.  They  have  not  as  yet  been  tried  in  the  multiple 
choice  apparatus  which  was  used  in  these  experiments.  The  maze  test,  and  the 
multiple  choice  as  well,  were  found  to  be  unsuited  to  the  average  native  equip- 
ment of  a  litter  of  seven  English  Bulldog  puppies  that  also  have  been  tested. 
Four  out  of  the  seven  dogs  failed  completely  to  learn  the  task,  sitting  in  a  corner 
of  the  maze  and  barking  disconsolately  at  the  gates.  They  held  back  from  pass- 
ing through  an  opening  through  which  an  average  mouse  would  at  once  venture. 
Two  of  the  dogs  learned  very  slowly,  while  one  made  a  good  record.  The  dogs 
were  more  interested  in  looking  for  the  experimenter  and  responding  to  the 
slightest  noise  he  would  inadvertently  make,  than  in  paying  attention  to  the 
maze  problem  itself. 


COBEELATION  IN  LEAENING  EECOEDS  25 

two  interference  trials  was  -f-  0.55 ;  and  for  the  same  period  in  the 
maze  test  with  the  last  ten  trials  of  the  interference  test  the  correla- 
tion amounted  to  -f  0.49. 

The  above  correlations  tend  to  show:  first,  that  the  animal  that 
does  well  in  any  one  task  is  likely  to  retain  more  than  one  that  does 
not  do  well ;  secondly,  time  and  error  are  closely  related  in  the  types 
of  behavior  that  this  investigation  deals  with,  and  one  is  a  measure 
of  the  other ;  thirdly,  an  animal  that  does  well  in  the  beginning  of  a 
task  is  more  likely  to  do  well  at  the  end  that  an  animal  that  is  slow 
in  learning;  fourthly,  the  animal  that  did  well  in  the  maze  task  ex- 
hibited greater  adaptability  in  behavior  than  one  that  did  not  do 
well,  as  shown  by  a  comparison  of  the  interference  records. 


VII.   FAMILY  RESEMBLANCES 

IN  the  preliminary  report  of  these  experiments  it  was  found  that 
the  mean  variation  of  the  entire  group  of  90  mice,  including  mice 
from  all  the  strains  that  had  been  tested  up  to  that  date,  amounted 
to  35.6.  This  means  that  any  mouse  picked  at  random  from  that 
group  would  be  likely  to  vary  from  the  average  by  35.6  seconds.  In 
order  to  find  whether  mice  of  the  same  litter  vary  less  than  unrelated 
individuals,  the  mean  variations  for  each  of  the  eighteen  families 
was  calculated,  and  these,  when  weighted  for  size  of  family,  were 
found  to  be  20.2.  It  was,  therefore,  stated  that  the  resemblance  in 
behavior  between  mice  belonging  to  the  same  litter  was  nearly  twice 
as  great  as  between  unrelated  individuals,  and  that  this  corresponded 
to  a  coefficient  of  correlation  in  the  neighborhood  of  0.5  for  brothers, 
as  found  by  Pearson,  Thorndike  and  others.  It  is  probable,  how- 
ever, that  in  this  case  the  mean  variation  was  increased  for  the  unre- 
lated individuals,  and  the  family  resemblance  correspondingly  made 
to  appear  greater,  due  to  the  fact  that  the  mixed  group  was  made 
up  of  two  fairly  distinct  strains  of  mice,  a  quick  white  group  and  a 
slow  yellow  group. 

As  previously  stated  the  above  calculation  was  made  from  the 
results  in  only  one  task,  namely,  the  initial  learning  period  of  fifteen 
trials  in  the  maze  test.  When  the  mean  variations  were  calculated 
for  the  four  distinct  tests  that  were  later  used,  and  in  which  con- 
siderably more  animals  were  tested,  there  was  apparently  no  greater 
resemblance,  judged  by  this  method  of  variation,  between  animals  of 
the  same  litter  than  between  unrelated  individuals.  In  order  to  dis- 
count the  inevitable  reduction  in  mean  variation  that  resulted  from 
the  grouping  of  the  individuals  into  family  lots,  in  which  case  the 
mean  variations  were  calculated  from  the  family  averages,  all  the 
mice  that  belonged  to  the  family  groups  were  rearranged  according 
to  chance  into  other  groups  of  exactly  the  same  size.  Then  the  mean 
variations  for  the  groups  formed  by  chance  arrangement  were  calcu- 
lated in  exactly  the  same  manner  as  was  previously  done  for  the  true 
family  groups.  A  comparison  of  the  two  results  showed  a  strict 
similarity  in  mean  variation  in  each  of  the  four  tests;  so  that  the 
mean  variation  for  the  groups  of  related  individuals  was  not  less 
than,  but  practically  identical  with  the  variation  that  obtained  for 
the  same  individuals  grouped  by  a  chance  arrangement.  Later  in 
this  thesis,  when  a  detailed  study  of  the  family  histories  is  taken  up, 
the  records  for  the  various  litters  will  give  further  light  on  this  sub- 
ject of  family  resemblances,  and  individual  variations. 


CORRELATION  IN  LEARNING  RECORDS 


27 


s  £ 


o» 


90*0399 


28       INDIVIDUAL  DIFFERENCES  AND  FAMILY  EESEMBLANCES 


VIII.   SEX  DIFFERENCES 


(a)  DIFFERENCES  IN  TIME  AND  ERROR  RECORDS 

IN  Table  IX.  the  males  and  females  are  grouped  separately,  and 
their  average  times  and  errors  are  given  for  the  various  tasks  that 
were  used.  The  preliminary  report  of  this  investigation  showed  that 
there  were  small  sex  differences  for  performance  in  the  initial  learn- 
ing period  in  the  maze  test,  and  the  differences  that  did  exist  were 

TABLE  IX 

AVERAGES  FOR  SEX  DIFFERENCES  AND  SEX  VARIABILITY 


Tests 

No.  and 
Sex 

Average  No. 
of  Sees, 
per  Trial 

Mean  Vari- 
ations In 
Seconds 

Probable 
Error 

Average  No. 
of  Errors 
perTria 

Initial  Learning  Period,  Maze  Test  .  . 
Interference  Test,  10  Trials 

93  & 
909 
34  d" 

43.80 

64.77 
3776 

33.5 
53.3 
290 

±2.9 

±4.7 
±43 

1.2 
1.7 

1  g 

Retention  Test 

379 
34  d" 

80.96 
27  58 

56.8 
21  8 

±8.0 
±32 

2.8 
1  4 

Multiple  Choice  Test 

379 
34  d" 

76.00 
25  76 

59.1 
170 

±8.3 
±25 

2.9 
28 

379 

52.08 

35.1 

±4.9 

3.9 

well  within  the  limits  of  the  probable  error.  With  a  larger  number 
of  animals,  93  males  and  90  females,  it  was  found  that  in  the  initial 
learning  period  in  the  maze  test,  the  males  did  considerably  better 
than  the  females.  The  males  made  an  average  time  per  trial  of 
43.80  ±  P.E.  2.9  seconds,  and  1.2  error  per  trial,  while  the  females 
made  a  corresponding  record  of  64.77  ±  P.E.  4.7  seconds  and  1.7 
error  per  trial.  As  previously  stated,  there  were  71  animals  that 
were  tested  in  the  interference,  retention  and  multiple  choice  tasks, 
and  of  these  34  were  males  and  37  females.  As  indicated  in  the  table 
for  sex  differences,  in  all  three  of  the  above  mentioned  tests  the 
females  took,  on  the  average,  twice  as  many  seconds  to  learn  the  tests 
and  made  considerably  more  errors  per  trial  than  did  the  males.  In 
the  interference  test  of  ten  trials  the  males  made  an  average  time  of 
37.76  ±  P.E.  4.3  seconds  and  1.6  error  per  trial,  while  in  the  same 
task  the  females  took  80.96  ±  P.E.  8.0  seconds  and  2.8  error  per  trial. 
The  retention  test  records  gave  a  similar  result;  the  males  making  an 
average  of  27.59  ±  P.E.  3.2  seconds  per  trial  and  1.4  error  per  trial, 
and  again  the  females  took  more  than  twice  as  long  to  perform  the 

29 


30      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

same  task,  namely,  76.00  ±  P.E.  8.3  seconds  and  2.9  error  per  trial. 
In  the  multiple  choice  test  the  males  took  25.76  ±  P.E.  2.5  seconds 
and  2.8  error  per  trial,  while  the  females  made  an  average  of  52.08  ± 
P.E.  4.9  seconds  and  3.9  error  per  trial.  The  final  average  of  the 
males  for  all  four  tests  amounted  to  33.72  ±  P.E.  4.9  seconds  per 
trial,  while  that  of  the  females  was  68.45  seconds.  This  shows  that 
the  females  in  the  total  record  took  slightly  more  than  twice  as  long 
to  learn  the  tests  as  did  the  males.12 

(&)  COMPARATIVE  DISTRIBUTIONS  OF  THE  MALES  AND  FEMALES 

In  Fig.  8  are  given  the  comparative  distributions  for  the  34  males 
and  37  females  that  have  been  tested  in  all  four  of  the  tasks  for 
which  time  averages  are  given  in  Table  IX.  The  distributions  for 
the  males  and  females,  in  the  initial  learning  period  of  the  maze  test, 
show  that  the  curve  for  the  males  is  skewed,  for,  although  there  is  an 
equal  number  of  individuals,  namely,  12,  between  0  and  20  seconds, 
and  20  and  40  seconds,  still  from  that  point  on  the  curve  drops 
quickly,  while  no  individuals  are  to  be  found  beyond  160  seconds. 
The  distribution  curve  for  the  females  shows  that  the  mode  for  that 
sex  is  about  the  same  as  that  found  for  the  males,  also  that  several 
females  are  distributed  toward  the  right  end  of  the  figure,  which 
indicates  that  they  were  the  animals  that  made  poor  time  records. 
Eight  females  are  to  be  found  between  0  and  20  seconds,  and  while 
the  curve  for  this  sex  drops  steadily  until  80  seconds  is  reached,  still 
it  rises  steadily  from  that  point  until  it  reaches  a  maximum  in  the 
region  between  140  and  160  seconds,  where  five  females  are  to  be 
found.  This  almost  gives  the  curve  a  bimodal  appearance,  but  there 
is  no  evidence  at  hand  which  leads  the  writer  to  believe  that  there 
were  two  distinct  classes  of  females  among  the  mice  that  were  tested. 
The  important  point  to  be  noted  in  Fig.  8  is  that  there  were  six 
females  that  exceeded  any  of  the  records  made  by  the  males;  there 

12  It  might  be  expected  that  this  sex  difference  would  have  its  effect  on  the 
validity  of  the  correlations  that  have  already  been  given,  since  they  show  that  the 
total  population  was  made  up  of  two  groups,  one,  the  males,  which  were  relatively 
quick  learners,  and  the  other  the  females,  relatively  slow  learners,  but  the  accom- 
panying correlations  that  were  made  for  the  separate  sexes  show  that  they  fol- 
low rather  closely  the  combined  correlations  that  have  been  given  in  Table  VIII. 
Correlating  the  last  15  trials  of  the  maze  test  with  the  first  two  trials  of  the 
interference  test  gave  the  following  correlations :  ^s  =  +  -60,  $s  =  +  .54.  The 
correlations  for  the  same  15  trials  of  the  maze  test  with  the  last  10  trials  of  the 
interference  test  gave :  ^s  =  +  .35,  $s  =  -f  .49.  Again  the  same  maze  trials  when 
correlated  with  the  retention  test  gave  the  following  correlations:  ^==  +  .18, 
$s  =  +  .27.  The  last  sex  correlation  was  made  between  the  last  15  trials  of  the 
maze  test  and  the  last  23  trials  of  the  multiple  choice  test,  and  here  the  following 
correlations  were  found:  Js  =  —  .26,  $s  +  .16. 


SEX  DIFFERENCES 


81 


were  two  females  between  180  and  200  seconds ;  one  between  200  and 
220  seconds;  one  each  between  240  and  260,  and  260  and  280  sec- 
onds ;  and  finally  one  female  that  failed  completely. 


10 


Test 


0  20      60      100 
No.  03  SCCONDS 


180     220     260     300     3W  360 


Test  oj  Tew  TriAl& 


020      60      100     m     ISO     220     260    300    3W  360 


"ReteNtioN  Test 


0  20      60      100      m     160     220     &0     300     3W  3401 


Multiple  Choice  Test 


0  20      60      /OO     m     J80     2^0     260     300    3W  360 

FIG.  8.  Distribution  Curves  for  the  Males  and  Females  for  all  Tasks.  In 
each  case  the  number  of  animals  is  given  by  the  ordinate,  while  the  abscissae 
represent  the  number  of  seconds  The  males  are  represented  by  the  solid  lines 
and  the  females  by  the  broken  lines. 


32      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

The  distribution  curves  for  the  males  and  the  females,  for  the 
interference  test  of  ten  trials  in  the  maze,  are  also  given  in  Fig.  8. 
Here  it  is  to  be  seen  that  the  curve  for  the  males  is  distinctly  skewed. 
Seventeen  males  are  grouped  between  0  and  20  seconds;  eight  be- 
tween 20  and  40  seconds,  and  from  there  on  the  curve  is  similar  to 
the  one  made  by  the  same  animals  in  the  initial  learning  period  of 
the  maze  test,  but  in  the  present  case  no  males  are  to  be  found  that 
took,  on  the  average,  longer  than  200  seconds  to  complete  the  test. 
This  figure  shows  that  the  mode  for  the  females  is  to  the  right  of  the 
mode  for  the  males;  the  greatest  number  of  females,  namely  nine, 
are  to  be  found  between  40  and  60  seconds.  The  curve  for  the  fe- 
males is  irregular,  again  showing  a  superiority  in  favor  of  the  males, 
while  here  two  females  failed  to  learn  the  test. 

The  distribution  curves  of  both  sexes  for  the  retention  test  show 
that  the  curve  for  the  males  is  similar  to  the  one  above  that  we  have 
just  examined.  It  is  skewed,  with  the  mode  between  0  and  20  sec- 
onds, where  twenty-one  animals  are  to  be  found,  while  no  records  for 
the  males  exceed  160  seconds.  The  curve  for  the  females  is  less 
skewed  than  that  of  the  males;  an  equal  number  of  individuals, 
namely  nine,  are  to  be  found  between  0  and  20  seconds,  and  20  and 
40  seconds ;  the  curve  then  drops  quickly,  but  rises  again  in  the  re- 
gion between  60  and  80  seconds,  where  there  are  six  animals.  Then 
the  curve  for  the  females  gradually  falls,  but  again  shows  the  same 
characteristic  that  is  to  be  found  in  all  the  comparative  distributions, 
namely,  that  a  number  of  females  are  distributed  beyond  the  max- 
imum records  made  by  the  males  in  the  same  test.  In  this  case  five 
females  made  longer  average  time  records  than  the  males,  and  two 
of  them  failed  to  learn  the  test. 

The  distribution  curves  for  the  males  and  females  in  the  multiple 
choice  test  are  given  at  the  bottom  of  Fig.  8.  Here  the  mode  for  both 
sexes  is  to  be  found  between  0  and  20  seconds ;  but  the  curve  for  the 
males  is  steeper  than  the  corresponding  one  for  the  females;  twenty 
males  being  found  between  0  and  20  seconds ;  seven  between  20  and 
40  seconds ;  five  between  40  and  60  seconds,  and  finally  two  between 
80  and  100  seconds,  which  is  the  maximum  time  record  for  the  males. 
The  distribution  curve  for  the  females  shows  eleven  individuals  be- 
tween 0  and  20  seconds,  and  then,  as  shown  in  the  figure,  the  curve 
drops  at  a  regular  rate ;  there  being  nine  individuals  in  the  next  time 
group,  seven  in  the  next,  four  in  the  next,  and  two  in  the  next,  where 
the  curves  for  both  sexes  meet.  It  is  to  be  noted,  however,  that  the 
same  thing  occurs  here  that  was  found  in  the  three  previous  distribu- 
tions, namely,  that  the  females  exceeded  the  maximum  time  records 


SEX  DIFFERENCES  33 

of  the  males  that  were  tested  with  them  at  the  same  time.  In  this 
case  one  female  is  to  be  found  in  each  of  the  following  time  regions : 
100  to  120  seconds ;  140  to  160  seconds ;  160  to  180  seconds,  and  260 
to  280  seconds. 

(c)  VARIABILITY  OP  THE  SEXES 

An  inspection  of  the  probable  errors  of  Table  IX.  indicates  that 
the  behavior  of  the  females  was  much  more  variable  than  that  of  the 
males.  The  table  gives  in  detail  the  variability  of  the  sexes.  In 
the  initial  learning  period  of  the  maze  test  the  following  record  was 
made:  mean  variation  males,  33.5  seconds;  mean  variation  females, 
53.3  seconds;  while  in  the  interference  test  of  ten  trials  the  mean 
variation  for  the  males  was  29.0  seconds;  and  for  the  females  56.8 
seconds.  The  corresponding  records  in  the  retention  test  gave  a  mean 
variation  for  the  males  of  21.8  seconds  and  for  the  females  59.1  sec- 
onds. In  the  multiple  choice  test  the  mean  variation  for  the  males 
amounted  to  17.0  seconds,  while  for  the  females  35.1  seconds.  The 
average  of  the  variations  for  all  the  tasks  amounted  to  25.3  seconds 
for  the  males  and  51.0  seconds  for  the  females.  These  figures  show 
that  the  variability  in  the  behavior  of  the  females  was  about  twice 
as  great  as  that  of  the  males. 

The  above  results  in  sex  differences  and  variations  agree  with 
those  of  Hubbert  in  her  work  on  habit  formation  in  the  albino  rat.13 
The  following  is  quoted  from  her  results:  "The  general  averages  for 
an  equal  number  of  males  and  females  show  the  males  superior  to 
the  females  in  all  points  save  one,  that  of  absolute  time.  They  fin- 
ished in  fewer  trials,  required  less  total  time,  and  covered  a  smaller 
amount  of  distance  in  learning  the  problem  than  did  the  females, 
while  their  speed  was  slightly  higher.  .  .  .  The  mean  variation  from 
the  time  average  is  less  for  the  males  at  all  ages,  their  distance  varia- 
tion is  less  at  the  age  of  sixty-five  days  and  three  hundred  days. ' ' 

Yerkes  found  that  for  the  behavior  of  the  dancing  mouse  in  the 
black-white  discrimination  tests:  "The  males  almost  invariably  ac- 
quired a  perfect  habit  quicker  than  the  females  .  .  .  (but)  ...  in 
the  labyrinth  test  the  female  is  as  much  superior  to  the  male  as  the 
male  is  to  the  female  in  the  discrimination  tests.  ...  A  degree  of 
proficiency  in  labyrinth  'B'  attained  by  the  males  after  7.0  trials  was 
equaled  by  the  females  after  6.2  trials.  In  labyrinth  *C'  the  males 
acquired  a  habit  as  a  result  of  18.7  trials ;  the  females,  as  a  result  of 
13.8.  And  similarly  in  labyrinth  'D,'  6.1  trials  did  no  more  for  the 
males  than  2.9  did  for  the  females. ' ' 

13  Hubbert:  "The  Effect  of  Age  on  Habit  Formation  in  the  Albino  Bat," 
Behavior  Monograph  Series,  No.  11,  1915. 


34       INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

The  results  of  the  present  investigation  agree  with  those  found  by 
Yerkes  concerning  his  discrimination  test,  but  do  not  agree  with  his 
results  for  the  labyrinth  test.  The  multiple  choice  used  in  the  pres- 
ent experiments  was  primarily  designed  to  test  discrimination,  while 
tending  to  destroy  position  habit,  and  so  it  may  be  considered  com- 
parable to  the  discrimination  test  used  by  Yerkes.  Here  there  is 
agreement,  in  that  the  males  did  better  than  the  females,  but  in  the 
maze  test,  which  corresponds  to  Yerkes'  labyrinth,  the  results  of  this 
investigation  agree  with  Hubbert  's  and  disagree  with  those  of  Yerkes. 


IX.   INDIVIDUAL  DIFFEEENCES  AND  METHODS   OF 
HABIT  FORMATION 

WE  may  now  take  up  in  more  detail  a  study  of  the  records  made 
by  a  few  of  the  animals  that  show  typical  or  exceptional  types  of 
behavior,  and  also  discuss  the  observations  made  on  the  methods  of 
habit  fixation.  In  Figs.  6  and  7  are  given  samples  of  practise  curves 
for  several  mice,  showing  the  daily  records  in  each  group  of  trials,  in 
the  order  that  they  were  given.  The  arrows  at  the  highest  points  on 
the  curve  indicate  that  the  mouse  did  not  pass  through  the  maze  or 
multiple  choice  test  within  360  seconds. 

In  Fig.  6  are  given  the  daily  record  curves  for  two  agouti  mice, 
131  Ag.  J*  and  132  Ag.  $.  Their  average  time  records  are  given  in 
Table  VI.  They  are  mice  from  a  single  litter  and  their  records  show, 
in  both  cases,  very  rapid  and  consistent  learning  in  the  maze  test, 
remarkably  slight  interference  effect  at  the  eighteenth  trial,  followed 
by  a  complete  recovery  and  very  speedy  time  records  from  the  twen- 
ty-first to  the  twenty-ninth  trial.  No.  131,  whose  record  is  indicated 
by  the  solid  line,  made  a  record  in  all  the  tasks  which  was  consider- 
ably better  than  the  average.  It  showed  a  very  strong  retention  for 
the  maze  test,  while  the  records  in  the  multiple  choice  test,  although 
very  good,  show  a  more  irregular  performance  than  in  the  maze  test. 
This  irregularity  of  performance  in  the  multiple  choice  test  appears 
typical  for  the  mice  that  have  been  tested  in  this  investigation,  and 
the  irregularity  may  be  due  to  the  factors  peculiar  to  the  test  itself, 
or,  as  previously  discussed,  to  interference  effects  from  previous 
training.  No.  132,  whose  record  is  indicated  in  Fig.  6  by  a  broken 
line,  failed  to  get  through  the  multiple  choice  test  for  the  first  five 
days;  succeeding  on  the  sixth  day,  it  made  fairly  good  records  there- 
after. These  two  mice  were  taken  as  examples,  because  they  typify 
the  characteristic  manner  in  which  good  time  records  were  made  by 
the  mice  that  were  tested  in  these  experiments.  The  writer  refers 
to  the  method  of  learning  by  rhythm  of  movements,  which  also  has 
been  noted  by  Watson,  Basset  and  others  for  white  rats.  It  was 
noted,  for  instance,  that  mouse  132  Ag  $,  in  the  initial  learning 
period  in  the  maze  test,  never  went  to  the  closed  gate  in  the  first  com- 
partment after  the  first  two  days  of  training.  For  a  week  of  learn- 
ing, from  the  fourth  trial  to  the  tenth  inclusive,  this  mouse  passed 
the  first  open  gate  successfully,  but  instead  of  going  on  to  the  open 
gate  in  the  second  compartment,  the  animal  invariably  made  a  detour 

35 


INDIVIDUAL  DIFFEEENCES  AND  FAMILY  RESEMBLANCES 


TABLE  X 
BHYTHM  IN  THE  PRODUCTION  OF  ERRORS  IN  THE  MAZE  TEST 


Record  for  131  Ag.  o" 

Record  for  132  Ag.   9 

No.  of 
Days 

No.  of  Times  to  Gates  In  Each 
Compartment 

No.  of 
Days 

No.  of  Times  to  Gates  In  Eacb 
Compartment 

Closed 

Open 

Closed 

Open 

1 
£ 

M 
a 

I 

3 
a 

B 

a 

£ 
9 

1 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 

8  

10 

1 
....12  

6 

1  Learning  Period 

1 

2 
3 
4 
5 
6 
7 
8 
9 
10 

1 
1  
2 
4  

4  
1  
1  
1  
1  

3 

2  
4 
4  
1 
3  
1 
1  
1 
1  
1 
1  
1 
1  
1 
1  
1 

1 

2 

2 

2 

1 

1 
1     

1  
1     . 

1 
1  
1 
1  
1 
1  
1 
1  
1 

1  
1  
1 

.  .  .1  

I 

2 

1 

"C 
-S 

^ 

11 

12 
13 

14 
15 
16 

17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 

1  
1  

1 
1 

1 

1 
1 

"  4'" 
.   l  

1 
1  

1 
3 

3 

1  
1 

"l"" 

"i" 

1 
1 

i 

i 
'"i" 
"i" 

i 

...1  

1 
1  

INDIVIDUAL  DIFFERENCES 


37 


Record  for  131  Ag.  d1 

Record  for  132  Ag.  9 

No.  of 
Days 

No.  of  Times  to  Gates  In  Each 
Compartment 

No.  of 
Days 

No.  of  Times  to  Gates  In  Each 
Compartment 

Closed 

Open 

Closed 

Open 

Retention 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 

1 
1  

1 
1  

Retention 

1 
2 
3 

4 
5 
6 
7 
8 
9 
10 

2 
1 

2 
1 

1 
.M.... 

1 

1 

1 

'"{'" 

1 

1 

"i" 

i 
"'2 

i 

l  

by  first  going  to  the  closed  gate  in  the  second  compartment  before 
completing  the  day's  record.  After  the  position  of  the  open  gate 
had  been  changed,  from  the  right  to  the  left  in  this  case,  at  the  inter- 
ference point,  i.e.,  the  eighteenth  day,  the  mouse  tried  to  pass  through 
the  previously  open  gates,  but  from  the  third  day  after  the  inter- 
ference had  been  given  a  new  rhythm  was  set  up,  which  lasted  until 
the  last  trial,  where  a  perfect  record  of  no  errors  was  made.  The 
rhythm  in  this  case  reversed  the  previous  rhythm  by  the  mouse  try- 
ing to  pass  through  the  closed  gate  in  the  first  compartment,  but  fail- 
ing to  pass  this  gate  it  quickly  ran  around  to  the  successful  gate  and 
dashing  through,  continued  on  to  the  open  gate  in  the  second  com- 
partment. As  will  be  shown  in  an  accompanying  table,  it  is  interest- 
ing to  note  that  this  mouse,  except  for  the  first  three  days  of  training 
and  the  first  two  interference  days,  made  only  a  single  error  on  any 
one  day.  In  Table  X.  are  given  the  daily  error  records  for  the  same 
two  mice,  Nos.  131  and  132,  that  were  made  in  the  maze  test.  The 
left  half  of  the  table  gives  the  complete  record  for  No.  131,  while 
at  the  right  is  given  the  record  of  No.  132.  The  first  column  gives 
the  number  of  days  and  indicates  the  extent  of  each  learning  period ; 
the  second  column,  the  number  of  times  that  each  mouse  tried  to 
pass  through  the  closed  gates  in  each  compartment  (if  two  numbers 
are  given  for  any  one  day  the  upper  number  represents  the  errors 
in  the  first  compartment  and  the  lower  one  errors  in  the  second  com- 
partment) ;  while  the  third  column  gives  the  number  of  trials  made 


38      INDIVIDUAL  DIFFERENCES  AND  FAMILY  EESEMBLANCES 

at  the  open  gates.  The  errors  are  thus  given  in  the  second  column 
for  each  mouse,  while  the  number  1  in  the  third  column  merely 
means  that  the  animal  has  successfully  passed  through  the  open 

gates.  The  record  indicated  in  the  table  by:  1  1  and  found  to 
occur  on  the  fourth  day  for  both  mice,  is  repeated  several  times  for 
each  animal.  This  rhythm  may  be  interpreted  by  saying  that  the 
animal  successfully  passed  the  first  open  gate,  without  making  any 
errors  in  the  first  compartment,  but  ran  around  to  the  closed  gate  in 
the  second  compartment  and  was  thus  credited  with  an  error  before 
it  finished  the  day's  record.  By  a  glance  at  the  table  it  will  be  seen 
that  the  single  error  that  was  made  in  the  second  compartment  was 
not  eliminated  until  the  tenth  day  for  mouse  No.  131,  and  one  day 
later  No.  132  made  a  perfect  record.  This  same  error  occurred  once 
more  on  the  fifteenth  day  for  No.  131,  and  of  the  twelfth  and  four- 
teenth day  for  No.  132.  These  examples  are  typical  in  that  they 
show  that  errors  in  an  animal's  behavior  are  not  suddenly  discon- 
tinued, but  are  gradually  eliminated.  Further,  it  may  be  noted  that 
after  only  two  days  of  the  interference  test,  the  eighteenth  and  the 
twentieth,  No.  131  changed  its  entire  movement  habit ;  after  only  six 
errors  it  was  able  to  make  the  correct  turn  to  the  left  in  each  com- 
partment, while  before  the  interference  was  set  the  correct  turn  had 
been  to  the  right.  This  record  shows  a  rather  unusual  amount  of 
flexibility  of  behavior;  only  a  few  animals  have  been  observed  to 
make  a  similar  record.  In  fact,  if  such  records  were  found  to  be 
common  in  animal  behavior  we  would  have  to  alter  our  conception 
of  a  kinesthetic,  or  muscle  sense  movement;  for  the  quick  readjust- 
ment as  exemplified  in  the  behavior  of  mouse  No.  131  would  hardly 
be  compatible  with  our  idea  of  such  a  sense.  The  observations  of  the 
writer  lead  him  to  believe  that  kinesthesis  was  the  all  important  ele- 
ment in  adjusting  the  movements  of  the  animals  that  were  observed 
in  this  investigation.  It  is  also  to  be  remembered  that  in  the  case  of 
No.  131  any  visual,  olfactory  or  gustatory  clews,  if  they  existed  as 
such  for  the  animal,  were  so  left  under  the  experimental  conditions, 
that  they  would  favor  the  production  of  errors  during  the  interfer- 
ence period  and  not  tend  to  their  elimination.  The  behavior  of 
mouse  No.  132  in  the  interference  period,  with  numerous  errors,  ap- 
pears to  be  the  more  general  type  of  animal  reaction. 

Turning  again  to  the  subject  of  the  fixed  rhythmic  type  of  be- 
havior it  may  be  seen  in  Table  X.  that,  in  the  case  of  No.  132,  the 
n       1  " 

record  which  is  indicated  by  1     1  in  the  initial  learning  period, 


INDIVIDUAL  DIFFERENCES  39 

"1      1" 

changed  to  1  in  the  interference  test,  and  this  particular  per- 
formance persisted  nearly  a  month  later  in  the  retention  period. 

It  has  been  noted  from  the  careful  study  of  each  animal's  be- 
havior, that  individual  errors,  or  tendencies  to  make  such  errors,  are, 
as  a  rule,  gradually  overcome,  that  a  wrong  movement  made  in  the 
first  few  trials  persists  throughout  several  succeeding  trials  in  a 
gradually  diminishing  extent.  One  mouse  persisted  in  turning  once 
to  the  left  gate  in  the  first  compartment,  when  the  gates  were  opened 
on  the  right  side.  It  continued  to  do  this  for  several  days,  when  it 
was  noted  that  it  began  to  go  only  part  way  to  the  left  gate;  then 
turning  around  it  took  the  successful  path.  This  mouse  never  com- 
pletely broke  the  habit,  but  in  the  end,  the  turn  to  the  left  had  de- 
generated into  a  quick  whirl  around  in  a  circle,  followed  by  a  dash 
through  the  proper  gates.  This  type  of  behavior  has  been  noted  by 
other  observers;  the  following  is  quoted  from  page  32  of  Basset's 
monograph:3  "As  in  the  maze  experiment,  many  of  the  inbred  rats 
were  subject  to  errors  which  persisted  throughout  the  experiment. 
In  particular  may  be  mentioned  one  rat  that  invariably  formed  a 
loop  in  the  course  from  the  entrance  to  the  point  of  operation." 

Fig.  7  gives  the  daily  record  for  mouse  No.  134,  Agouti  $,  whose 
average  time  records  are  given  in  Table  VI.  This  record  shows  an 
initial  set  of  seventeen  trials  in  the  maze  test  that  almost  duplicates 
the  theoretical  learning  curve.  The  daily  record  for  eight  days, 
from  the  .tenth  trial  to  the  eighteenth,  which  marked  the  application 
of  the  interference  test,  shows  that  the  animal  approximated  the 
physiological  limit  of  performance;  taking  an  average  time  of  one 
second  per  trial  and  making  no  errors  at  all  during  that  period.  The 
interference  effect  for  the  animal  is  slight,  as  shown  by  the  first 
group  of  two  trials,  the  remaining  ten  trials  of  the  interference  are 
a  little  irregular,  but  the  noticeable  individual  difference  in  the  be- 
havior of  this  mouse  is  to  be  seen  from  the  very  poor  record  it  made 
in  the  multiple  choice  test.  It  did  not  make  a  successful  trip  in 
that  test  until  the  sixth  day  and  then  failed  for  eleven  consecutive 
days,  from  the  eighth  to  the  eighteenth  day,  inclusive,  and  also  failed 
on  the  twenty-second  day.  During  all  these  trials  the  animal  ap- 
peared to  be  in  very  good  health,  it  was  active  in  the  apparatus  as 
well  as  in  its  nest  box  and  made  plenty  of  errors  in  testing  the  col- 
ored doors.  It  is  tempting  to  speculate  that  the  poor  records  of  this 
mouse  in  the  multiple  choice  test  were  due  to  an  interference  effect 
carried  over  from  the  previous  training  in  the  maze,  but  perhaps  the 
relatively  poor  retention  test  that  followed  would  seem  to  disprove 


40      INDIVIDUAL  DIFFERENCES  AND  FAMILY  BESEMSLANCES 

this  assumption.  This  case  indicates  that  an  experimenter  can  pre- 
dict the  actions  of  an  animal  to  only  a  limited  degree,  for,  after  mak- 
ing consistantly  good  records  in  any  one  task,  some  external  or  in- 
ternal factors,  unknown  to  the  investigator,  may  become  operative 
and  break  up  the  expected  sequence  of  learning.  It  also  emphasizes 
the  importance  of  testing  an  animal  in  more  than  one  task  before  we 
finally  grade  its  behavior. 

If  space  permitted  it  would  be  interesting  to  give  in  detail  the 
learning  curves  of  mice  that  illustrate  still  other  kinds  of  individual 
differences.  It  may  be  well  to  call  attention  to  the  average  records 
of  mouse  No.  147  (see  Table  III.),  that  failed  completely  to  make 
a  successful  trip  through  the  maze,  although  it  was  tried  in  every 
one  of  the  tests.  It  finally  succeeded  in  making  the  poor  average 
record  of  159  seconds  in  the  multiple  choice  test,  but  when  retested 
at  the  time  the  retention  test  was  given  to  the  other  mice,  it  again 
failed  completely  in  the  maze  test.  Because  of  the  great  amount  of 
individual  differences  among  the  animals,  it  is  difficult  to  find  the 
record  of  a  single  mouse  that  made  a  record  that  was  similar  to  the 
average  for  each  task.  Only  No.  133,  whose  averages  are  given  in 
Table  VI.,  and  No.  189,  in  Table  III.,  approximated  an  "average" 
record.  The  record  of  No.  142,  in  Table  III.,  is  interesting  in  that 
it  shows  consistently  uniform  performance  throughout  all  the  tasks. 
This  mouse  made  the  following  averages:  36  seconds  in  the  initial 
learning  period,  24  seconds  for  the  first  two  interference  trials,  36 
seconds  for  the  last  ten  interference  trials,  35  seconds  for  the  mul- 
tiple choice  test,  and  33  seconds  for  the  retention  test.  Another 
type  of  animal  behavior  is  to  be  seen  in  the  case  of  mice  that  made 
very  poor  records  in  the  initial  maze  tests,  and  good  records  in  the 
multiple  choice  and  retention  tests.14 

The  multiple  choice  test,  which  did  not  favor  the  production  of  a 
stereotyped  form  of  reaction,  nevertheless  showed  some  interesting 
types  of  individual  and  group  responses.  It  was  found  that  the 
animals  exhibited  three  types  of  behavior,  which  were  not  definite, 
but  merged  one  into  the  other,  so  that  an  animal  might  use  one  of 
them  on  a  certain  day  and  another  type  on  the  next.  The  types  of 
reactions  were  as  follows : 

Type  1. — Response  by  slowly  and  carefully  "examining,"  visu- 
ally or  otherwise,  each  of  the  colored  doors,  very  suddenly  becoming 
oriented  and  dashing  through  the  successful  red  gate. 

Type  2. — The  animal  would  react  by  trying  the  gates  in  a  definite 

14  See  records  of  the  following  mice  in  Table  III.,  Nos.  138,  153,  154,  165, 
171,  178,  181,  187,  188,  206,  207,  209,  210,  211,  212,  and  in  Table  IV.,  No.  169. 


INDIVIDUAL  DIFFEEENCES  41 

order,  from  right  to  left,  or  left  to  right,  but  going  through  the  un- 
locked door  as  soon  as  it  was  reached. 

Type  3. — Kesponding  by  trying  the  gates  once  each,  in  an  irregu- 
lar manner,  and  finally  going  through  the  right  gate  apparently  by 
chance. 

It  was  noted  that  the  majority  of  the  animals  that  were  observed 
in  this  investigation  used  types  2  and  3  interchangeably.  A  few 
animals  used  type  1  for  several  days  in  succession  and  appeared  to 
actually  discriminate  before  they  made  their  final  choice  of  the  gates. 
This  type  1  reaction  was  noted  by  Burtt  in  his  experiments  entitled, 
"A  Study  of  the  Behavior  of  the  White  Rat  by  the  Multiple  Choice 
Method."15  In  the  case  of  one  rat  he  says:  ''In  problem  1  she  would 
at  times  become  oriented  very  suddenly,  dash  to  the  right  end  and 
then  across  to  the  correct  door. ' '  Types  2  and  3  of  this  investigation 
correspond  to  the  B  and  C  types  found  by  Hamilton  in  the  study  of 
primates  and  rodents.2 

is  Harold  C.  Burrt,  "A  Study  of  the  Behavior  of  the  White  Eat  by  the  Mul- 
tiple Choice  Method,"  Journal  of  Animal  Behavior,  May,  1916,  Vol.  6,  No.  3. 


X.   HEALTH  CONDITIONS  AND  LEARNING  ABILITY 

IT  is  generally  conceded  that  bodily  changes  in  the  general  health 
of  an  animal  may  greatly  tend  to  interfere  with  the  formation  of 
habits.  This  investigation,  however,  has  shown  that  a  number  of  ani- 


tKe 


Trials 


10 


FIG.  9.     Daily  Eecord  Curve  for  156,  White  d,  that  gave  good  records  although 
stunted   and  very  ill   throughout   all   the   test. 

mals  have  made  exceedingly  good  records  although  they  were  appar- 
ently in  very  poor  health.  They  were  put  through  the  tests,  more 
out  of  curiosity  to  see  what  they  would  do  than  for  anything  else, 
and  the  experimenter  was  surprised  to  find  them  making  very  good 

42 


HEALTH  CONDITIONS  43 

records  up  to  the  very  day  they  died.  An  example  of  such  a  case  is 
shown  in  Fig.  9,  which  gives  the  daily  record  of  No.  156,  White  c?, 
who  although  stunted  and  very  ill  throughout  the  experiment,  never- 
theless made  good  records.  This  mouse  did  not  seem  to  care  for  the 
reward,  which  was  the  food  to  be  found  at  the  end  of  a  successful 
trip,  and  when  it  returned  to  its  next  box  it  suddenly  became  very 
inactive,  and  did  not  appear  to  arouse  itself  again  until  it  was  tested 
the  following  day.  The  tables  also  indicate  the  incomplete  records 
of  several  mice  that  made  good  records  up  to  the  time  of  their  death, 
and  show  that  when  a  habit  is  once  firmly  fixed  it  may  resist  a  good 
deal  of  distracting  influences. 


XI.   FAMILY  HISTORIES 

WE  may  now  take  up  in  detail  the  family  histories.  Fig.  10  gives 
a  graphic  representation  of  matings,  from  which  were  selected  two 
mice,  No.  20  Y  $  and  No.  26  Y  $,  that  made  the  unusually  poor 
records  of  115  and  183  seconds  respectively,  though  the  other  mice 
in  the  same  litters  had  good  records.  The  parentage  of  Nos.  20  and 
26  was  unknown ;  they  were  mated  and  gave  two  litters,  each  com- 
posed of  three  males  and  one  female.  Three  mice  in  these  two  litters 
gave  unusually  slow  records  and  made  considerably  more  errors  than 
normal.  Two  other  mice  gave  poor  records;  two  gave  good  records, 
while  one  died  before  it  was  tested.  It  is  unfortunate  that  both  fe- 
males in  these  litters  died  before  further  offspring  could  be  obtained. 
Table  1  gives  the  complete  record  of  both  time  and  error  averages 
for  these  mice.  It  is  a  question  whether  or  not  selection  of  parents 
having  poor  records  tended  to  produce  more  than  the  normal  number 
of  offspring  slow  to  learn.  Further  investigation  can  alone  afford  an 
answer. 

The  mice  whose  records  are  given  in  Tables  II.  and  III.  are 
graphically  represented  in  Figs.  11  to  14  inclusive.  They  have  been 
carried  down  to  the  eighth  generation  and  are  still  being  tested. 
These  animals  are  related  and  compose  a  group  which  is  here  called 
the  white  family.  The  matings  began  from  an  original  pair  of  albino 
mice  that  were  purchased  from  a  dealer  in  the  spring  of  1913.  The 
records  for  the  parents  and  the  first  six  generations  are  given  in  Fig. 
III.,  and  it  is  to  be  noted  that  the  time  averages  for  the  animals, 
whose  catalogue  numbers  are  lower  than  128,  are  based  upon  per- 
formance only  in  the  initial  learning  period  in  the  maze  test.  The 
time  records  for  all  the  animals  of  the  F7  and  F8  generations,  and 
one  family,  Nos.  135  to  138  in  the  F6  of  Fig.  12,  are  based  on  an 
average  performance  in  all  the  tests  as  previously  explained.16  The 
parents  of  the  white  family,  Nos.  8  and  9,  were  quick  to  learn,  mak- 
ing averages  of  thirteen  and  eighteen  seconds  respectively.  The  first 
generation  was  composed  of  four  mice,  one  was  not  tested,  two  took 
considerably  longer  to  learn  the  test  than  either  of  the  parents,  while 
the  remaining  animal  made  a  quick  record.  The  family  average 
equalled  59.7  ±  P.E.  15.7  seconds.  A  successful  mating  was  ob- 

"The  average  time  for  the  71  mice  that  was  calculated  upon  performance 
in  all  tasks  was  55.&  ±  P.E.  3.5  sec.,  and  this  was  practically  identical  with  the 
average  time  made  by  the  183  mice  that  was  based  on  the  records  for  only  the 
initial  learning  period  of  the  maze  test;  namely,  54.1  ±  P.E.  2.3  sec. 

44 


FAMILY  HISTORIES 


45 


^e 


46       INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

tained  from  the  two  mice  that  made  the  slow  records,  and  the  result- 
ing litter  of  five  females  and  one  male  composed  the  second  genera- 
tion of  the  white  family.  All  the  mice  of  this  litter  gave  time  records 
that  were  better  than  the  average,  so  that  the  family  time  was  very 
good,  amounting  to  23.3  ±  P.E.  5.6  seconds.  A  glance  at  the  chart 
will  show  that  the  majority  of  the  mice  of  this  second  generation 
tended  to  resemble  their  grandparents  rather  than  their  parents. 
No.  48,  the  male  of  the  litter,  was  quick  to  learn  and  made  an  average 
time  of  ten  seconds.  He  mated  with  two  of  the  females  of  the  same 
litter,  namely,  No.  50,  that  made  an  average  of  20  seconds,  and  No. 
51,  with  an  average  of  9  seconds.  From  these  two  matings  two 
litters  were  obtained  that  compose  the  third  generation  of  the  strain. 
All  the  mice  in  these  litters  made  poorer  records  than  either  of  their 
parents,  and  thus  reversed  the  condition  that  occurred  between  first 
generation  parents  and  second  generation  offspring,  that  we  have 
just  examined.  The  offspring  of  No.  48  X  No.  50  were  two  females 
and  one  male.  The  male,  No.  66,  made  the  very  poor  average  of  113 
seconds,  while  one  female  took  35  seconds,  and  the  other  75  seconds. 
Four  offspring  of  this  generation,  three  males  and  one  female,  re- 
sulted from  the  mating  of  No.  48  X  No.  51,  while  here  again  one  of  the 
males,  No.  78,  made  the  poor  record  of  122  seconds,  one  other  male, 
No.  77,  took  68  seconds,  and  the  female,  No.  76,  made  an  average  of 
31  seconds.  The  remaining  male  died  before  it  could  be  tested.  It 
will  thus  be  seen  that  from  the  mating  of  No.  48  with  two  females, 
two  litters  were  obtained  that  gave  almost  identical  family  averages ; 
the  average  for  Nos.  65,  66,  and  67  was  74.3  ±  P.E.  15.9  seconds, 
while  the  average  for  Nos.  76,  77,  and  78  was  73.7  ±  P.E.  19.5  sec- 
onds. The  only  litter  that  was  successfully  raised  to  continue  the 
fourth  generation  of  the  strain  was  obtained  by  back  crossing  No.  66, 
who  made  the  poor  average  of  113  seconds,  with  his  own  parent  No. 
50,  with  the  quick  average  of  20  seconds.  Their  offspring  composed 
a  litter  of  two  males  and  two  females.  One  of  the  males  died;  the 
other  made  an  average  record  of  53  seconds ;  one  female  made  a  good 
record  of  24  seconds ;  while  here  again,  as  in  the  two  previous  litters, 
a  single  mouse,  No.  72,  made  a  poor  average  of  121  seconds.  The 
family  average  for  these  three  mice  was  66  ±  P.E.  22.3  seconds.  No. 
71  mated  with  No.  72,  but  only  a  single  male,  No.  91,  was  saved  from 
their  litter  to  stand  as  the  sole  representative  of  the  fifth  generation. 
No.  91  made  an  average  time  of  38  seconds,  and  was  destined  to 
become  the  paternal  parent  of  a  considerable  number  of  offspring. 
As  neither  of  the  females  of  the  fourth  generation  mated  with  No. 
91,  he  was  mated  successfully  with  four  unrelated  white  females, 


FAMILY  HISTOEIES 


47 


X(/8 


No.8w 


NO.OW    No-Asrw  NO  /few 

M  1  1  y  AverAGe  -59.7*  /4T.7  Sec. 


N.  ^A 


@©0©@ 


Ko./O5w 
*  /^*o 

FIG.  11.     Descent  of  a  White  Family. 


48      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

Nos.  86,  87,  88,  and  89.  These  females  had  been  previously  tested 
and  found  to  give  exceptionally  good  records  as  indicated  in  Table 
II.  Twenty-seven  offspring  resulted  from  these  matings.  Their  rec- 
ords are  remarkably  uniform  and  the  family  averages  are  among 
the  lowest  so  far  obtained.  The  result  of  crossing  No.  91  with  No. 
89,  who  made  the  quick  average  of  12  seconds,  is  shown  as  the  sixth 
generation  in  Fig.  14,  which  is  composed  of  two  males  and  two  fe- 
males. These  mice  were  uniformly  quick  to  learn,  making  averages 
of  8,  12,  11  and  15  seconds,  with  a  family  average  of  14  ±  P.E.  0.6 
seconds. 

Fig.  12  represents  a  continuation  of  the  history  of  the  white 
family  resulting  from  the  mating  of  No.  91  with  No.  87,  that  made  a 
good  time  record  of  15  seconds.  These  mice  produced,  in  the  sixth 
generation,  two  litters,  the  first  of  which  was  composed  of  five  males 
and  two  females  that  made  exceptionally  quick  and  uniform  records, 
and  showed,  as  in  the  previous  mating  that  we  have  just  discussed,  a 
considerable  amount  of  family  resemblance.  Their  family  average 
amounted  to  13.1  seconds  with  the  low  P.E.  of  1.7.  It  is  to  be  noted 
that  three  of  the  mice  of  this  litter  made  an  average  of  eight  seconds, 
.two  an  average  of  twelve  seconds,  one  an  average  of  16  seconds, 
and  another  28  seconds.  The  second  litter  of  No.  91  X  No.  87  gave 
two  males  and  two  females,  and  again  good  records  were  made  by  all 
but  one  of  the  mice,  No.  138,  that  made  an  average  of  76  seconds. 
The  other  mice  gave  average  time  records  of  23,  9  and  11  seconds 
respectively,  while  the  family  average  amounted  to  29.7  ±  P.E.  11.4 
seconds.  The  seventh  generation  of  this  particular  branch  of  the 
white  family  was  composed  of  three  different  matings  of  the  sixth 
generation  mice.  No.  115,  with  an  average  of  12  seconds,  was  crossed 
with  No.  118  that  made  a  similar  average.  Their  offspring  are 
shown  at  the  left  of  Fig.  15,  and  two  litters  were  obtained  from  the 
same  mice.  The  first  litter  gave  a  family  average  of  41.1  ±  P.E.  7.5 
seconds,  and  the  members  of  this  family  made  fairly  low  and  uniform 
records,  except  in  the  case  of  No.  143,  that  made  a  poor  time  average 
of  100  seconds.  Four  of  the  other  mice  made  records  in  the  neigh- 
borhood of  30  seconds  and  one  took  16  seconds.  It  is  a  curious  fact 
that  in  each  of  the  litters  of  the  seventh  generation  of  this  branch  of 
,the  white  family  there  was  a  single  female  that  made  time  records 
that  were  considerably  poorer  than  any  of  the  records  made  by  the 
males  of  the  same  litters.  It  will  be  also  found  that  this  condition 
holds  to  a  limited  extent  for  the  two  other  (branches  of  the  strain  that 
will  be  given  later  in  Figs.  13  and  14.  This  irregularity  in  the  be- 
havior of  the  females  tended  to  increase  the  mean  variations  for  the 


FAMILY  HISTOBIES 


49 


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NO./9AW  No.l9t 
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50      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

litters  and  to  decrease  the  family  resemblances,  while  it  accounts  for 
the  rather  large  sex  difference  that  has  already  been  discussed.  The 
second  litter,  resulting  from  crossing  No.  115  with  No.  118,  gave  two 
males  that  made  averages  of  21  and  24  seconds  respectively,  one  fe- 
male that  died,  and  again  a  very  slow  female  that  made  an  average 
of  132  seconds.  The  family  average  was  59  ±  P.E.  29.5  seconds. 
The  middle  group  of  seventh  generation  mice  that  is  given  in  Fig.  12, 
resulted  from  two  successful  matings  of  a  male,  No.  136,  with  an 
average  record  of  9  seconds,  with  No.  138  whose  average  was  76  sec- 
onds. It  may  be  seen  that  in  the  first  litter,  Nos.  190  to  195  inclusive, 
all  the  males  and  one  female  made  good  records,  while  again,  as  was 
found  in  the  previous  litters  of  this  generation,  one  female  made  ex- 
ceptionally poor  records.  This  was  the  case  of  No.  195  that  made  an 
average  of  265  seconds.  The  family  average  amounted  to  65  ±  P.E. 
25.6  seconds.  The  litter  that  was  subsequently  obtained  from  the 
same  parents  gave  three  males  that  made  good  records,  22,  28  and 
29  seconds,  respectively,  and  three  females  that  made  time  averages 
considerably  slower  than  the  average  for  the  entire  population.  One 
female  made  an  average  of  75  seconds,  another  91  seconds,  and  still 
another  106  seconds.  Again  it  may  be  noted  that  the  females  fell 
behind  the  males  in  quickness  of  learning.  The  family  average  of 
the  second  litter  is  similar  to  the  first,  and  amounted  to  58.5  ±  P.E. 
12.3  seconds.  It  is  hoped  that  sufficient  data  may  be  later  obtained 
to  show  whether  or  not  there  is  a  closer  resemblance  between  litters 
belonging  to  the  same  parents  than  between  unrelated  litters,  and 
also  to  determine  whether  or  not  mice  belonging  to  the  first  litters  of 
any  two  young  parents  tend  to  be  superior  or  not  to  the  mice  that  are 
produced  from  these  same  parents  when  they  are  considerably  older 
and  have  produced  several  litters  of  mice.  The  number  of  double 
litters  that  has  been  obtained  in  these  experiments  is  hardly  large 
enough  to  warrant  any  conclusion  on  this  point,  but  it  may  be  noted 
that  several  of  the  cases  that  have  been  found  show  that  the  family 
averages  of  first  and  second  litters  overlap  when  due  consideration 
is  given  to  the  size  of  the  probable  error  that  is  attached  to  each 
average.  No.  136  and  No.  137,  that  made  very  good  time  records, 
were  mated,  and  they  added  two  more  mice  to  the  seventh  generation 
of  the  white  family;  one  of  them,  a  male,  made  an  average  of  19 
seconds  and  the  other,  a  female,  took  59  seconds.  Their  combined 
average  amounted  to  44  ±  P.E.  21.2  seconds. 

In  order  to  study  another  branch  of  the  white  family  we  must 
again  go  back  to  the  fifth  generation  and  note  what  resulted  from 
mating  No.  91  with  another  white  female,  namely  No.  86,  that  also 


FAMILY  HISTORIES 


51 


made  a  quick  time  record  of  15  seconds.  The  records  for  this  branch 
of  the  strain  are  given  in  Fig.  13.  As  in  the  other  branch  we  have 
just  discussed,  No.  91  again  produced  an  exceptionally  quick  and 
uniform  family  in  the  sixth  generation.  This  litter  was  composed  of 
three  males  and  three  females,  Nos.  122  to  127  inclusive.  Four  in 
the  litter  made  time  averages  of  fifteen  seconds  or  lower,  while  the 
other  two  took  32  and  33  seconds  each.  Their  family  average 
amounted  to  19.1  ±  P.E.  3.4  seconds.  No.  125,  with  an  average  of  9 


>(0/57w    No'58w  Nc>.y?w    No'Ww  No)55w    Nol5/w     NO/5SW   No;53WNo/5y 


FIG.  13.    Continuation  of  the  White  Family,  No.  91  mated  with  No.  86. 

seconds,  and  No.  127,  whose  average  was  15  seconds,  were  mated  and 
they  produced  in  the  seventh  generation  two  litters.  The  first  was 
composed  of  six  mice,  Nos.  155  to  160  inclusive ;  two  were  males  and 
four  females.  All  these  mice  made  averages  slower  than  any  of  their 
sixth  generation  kin.  One  male  made  an  average  of  62  seconds,  two 
females  gave  average  records  of  about  90  seconds,  one  of  44  seconds 
and  another  of  49  seconds.  The  family  average  here  was  fairly  high, 
amounting  to  66.4  ±  P.E.  7.6  seconds.  The  second  litter  was  com- 
posed of  two  males  and  three  females,  but  Nos.  172  and  173  died  be- 


52      INDIVIDUAL  DIFFEBENCES  AND  FAMILY  BESEMBLANCES 

fore  they  could  be  tested,  while  No.  174  did  not  complete  its  record. 
The  ineompleted  records  of  this  mouse  are  given  in  Table  III.  The 
one  male  that  lived,  No.  171,  gave  an  average  of  55  seconds  and  the 
female  made  an  average  of  125  seconds.  Their  combined  average 
equalled  90  ±  P.E.  29.7  seconds.  Once  again  it  may  be  noted  that 
the  female  was  the  one  that  made  the  comparatively  poor  time  record. 
The  other  litter  of  the  seventh  generation  was  obtained  from  mating 
No.  123,  whose  average  was  32  seconds,  with  No.  126,  whose  average 
was  12  seconds.  Their  offspring,  Nos.  150  to  154  inclusive,  compose 
a  litter  of  one  male  and  four  females,  one  mouse,  No.  153,  did  not 
quite  complete  its  record  (see  Table  III.).  The  male  of  this  litter, 
No.  150,  made  a  poor  average  record  of  102  seconds,  and  it  is  worth 
calling  attention  to  the  fact  that  its  case  is  the  only  one,  among  all 
the  sixth,  seventh,  or  eighth  generations,  where  a  male  has  made  a 
very  poor  record.  Two  females,  Nos.  151  and  152,  made  good  records 
of  26  and  27  seconds  each,  while  the  remaining  female  made  an  aver- 
age of  60  seconds.  The  family  average  in  this  case  was  53.7  ±  P.E. 
13.4  seconds.  The  matings  for  the  eighth  generation  have  only  just 
been  started ;  one  litter,  however,  Nos.  208,  to  213  inclusive,  has  been 
obtained  by  crossing  No.  155,  a  male,  with  a  time  average  of  62  sec- 
onds, with  No.  143,  whose  average  was  100  seconds.  Their  offspring 
were  six  in  number,  two  males  and  four  females.  One  male,  No.  208, 
died,  but  its  incomplete  records  are  given  in  Table  III.,  and  the  re- 
maining male,  No.  209,  made  an  average  record  of  36  seconds.  One 
female,  No.  213,  gave  a  good  average  of  13  seconds,  while  the  other 
three  females  ranged  from  50  to  82  seconds.  The  average  family 
record  amounted  to  48.2  ±  P.E.  8.0  seconds. 

The  fourth  .and  last  branch  of  the  white  family  is  given  in  Fig. 
14.  Here  it  may  be  seen  that  No.  91  was  mated  with  another  female, 
No.  88,  that  made  the  very  quick  average  record  of  9  seconds.  The 
sixth  generation  litter  of  four  males  and  two  females  that  was  ob- 
tained from  this  mating  made  the  best  family  record  that  has  so  far 
been  obtained,  namely,  12  ±  P.E.  1.0  second.  None  of  the  mice 
made  an  average  time  record  exceeding  20  seconds.  It  is  an  inter- 
esting point  that  all  but  one  of  the  27  offspring  of  No.  91  made  time 
records  considerably  superior  to  the  average.  Three  matings  were 
made  from  these  sixth  generation  mice.  No.  116,  a  male,  was  crossed 
with  No.  121,  and  these  two  mice  made  average  records  of  10  and  12 
seconds  respectively.  Two  seventh  generation  litters  were  obtained 
from  them.  The  first  litter,  Nos.  161  to  166  inclusive,  was  com- 
posed of  three  males  and  three  females,  with  a  family  average  of 
34.3  ±  P.E.  7.4  seconds.  Two  of  the  males  made  good  records  of  14 


FAMILY  HISTOBIES 


53 


sD 

V. 


54      INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 


(UNKNOWN) 


83 

% 

56 

DICD 

37 

(^ 

N0.32Y     No33Y     No3*Y     No  35Y   No.36Y     No.37Y 


FIG  15.     Descent  of  a  Family  of  Mice  consisting  mostly  of  Yellow  Individuals. 

and  18  seconds,  while  one  gave  a  record  of  71  seconds;  two  females 
also  made  good  records,  and  one  an  average  record.  None  of  the 
mice  in  this  litter  made  records  as  low  as  either  of  their  parents. 
The  second  litter  of  No.  116  X  No.  121  was  rather  large,  composed  of 
ten  mice,  but  three  of  the  seven  males  died  before  their  records  were 
completed  (see  Table  III.  for  records  of  Nos.  180,  183  and  185),  and 
one  male,  No.  184,  died  before  the  tests  began.  Three  of  the  males 
and  one  female  that  completed  their  records  made  fairly  quick  aver- 
ages, while  two  females  gave  time  averages  of  98  and  83  seconds. 
The  family  average  amounted  to  53  ±  P.E.  9.6  seconds.  When  No. 
116  was  mated  with  No.  120,  whose  average  was  11  seconds,  a  sixth 
generation  litter  of  four  mice  resulted ;  two  were  males  and  died  be- 
fore their  records  were  completed  (see  Table  III.  for  records  of  145 
and  146),  and  one  female,  No.  147,  gave  the  very  poor  record  of  210 
seconds.  This  was  the  female  that  failed  completely  in  all  the  maze 


FAMILY  HISTORIES 


55 


tests,  while  the  other  female,  No.  148,  made  a  poor  record  of  72  sec- 
onds. It  is  to  'be  noted  again  that  in  the  seventh  generation  of  this 
branch  of  the  white  family,  four  of  the  females  made  time  records 
inferior  to  any  of  those  made  by  the  males  of  the  same  generation. 
Another  family,  mostly  of  yellow  mice,  was  derived  from  a  yellow 
female  and  an  unknown  male,  probably  white.  The  first  generation 
from  this  mating  gave  a  litter  of  six,  Nos.  32  to  37  inclusive.  The 
records  of  five  of  these,  one  having  died,  are  given  in  Table  IV.  and 
are  graphically  represented  in  Fig.  15.  This  litter  gave  a  family 
average  of  56.6  ±  P.E.  10.1  seconds.  Two  of  the  males,  Nos.  32  and 
33,  made  poor  records;  No.  34,  an  average  record  of  56  seconds; 
while  the  remaining  male  made  a  fairly  good  record  of  37  seconds. 
No.  37,  the  only 'female  of  this  litter,  gave  a  record  of  17  seconds; 
she  mated  but  once,  and  it  is  not  known  with  which  brother.  She 
bore  in  the  second  generation  two  females  and  'a  male,  Nos.  54,  55 
and  56.  One  female,  No.  54,  made  a  record  of  35  seconds,  while  the 
other  female  made  a  poor  record  of  112  seconds.  The  male,  No.  55, 
also  did  poorly  with  an  average  of  150  seconds.  No.  54  and  No.  56 


11 

16 

16 

6 

No.lfc7Y     Na/68Y    N<xl«BI. 

/PAAAI»y  AverAG 

FIG.  16.     Descent  of  a  Family  of  Mice  composed  of  Colored  Individuals. 


56       INDIVIDUAL  DIFFERENCES  AND  FAMILY  RESEMBLANCES 

were  both  crossed  with  No.  55,  and  two  litters  resulted.  No.  55  X  No. 
56  gave  Nos.  68,  69  and  70  in  the  third  generation,  and  No.  55  X  No. 
54  gave  Nos.  61  to  64  inclusive.  From  a  survey  of  the  complete 
records  of  these  mice,  it  is  seen  that  although  the  second  and  third 
generations  came  from  the  female,  No.  37,  which  made  the  excep- 
tionally low  record  of  17,  still,  two  of  her  young  in  the  second  gen- 
eration made  poor  records,  and  Nos.  61,  65  and  70  in  the  following 
generation  did  the  same. 

The  last  family  history  that  will  here  be  discussed  is  composed  of 
another  strain  of  colored  mice  that  began  from  a  mating  of  two  yel- 
low mice.  The  records  for  these  individuals  are  given  in  Table  VI. 
and  are  graphically  represented  in  Fig.  16.  This  family  was  started 
in  order  to  see  whether  there  was  any  real  correlation  between 
strains  of  colored  mice  and  their  ability  to  learn  quickly  and  to 
adapt  themselves  to  varied  conditions.  It  was  especially  desired  to 
test  the  learning  ability  of  a  greater  number  of  yellow  mice,  and  to 
this  purpose  the  two  founders  of  the  family,  Nos.  98  'and  99,  were 
both  yellow  mice  that  came  from  the  same  yellow  strain  that  had 
previously  exhibited  individuals  that  were  very  slow  to  learn.  It 
was  also  desired  that  a  further  study  of  the  effects  of  close  inbreeding 
be  carried  on  independently  of  the  other  problem,  and  for  this  pur- 
pose certain  strains  of  the  family  are  now  being  bred  with  this  object 
in  view.  The  inbreeding  in  this  investigation  has  not  been  carried 
on  close  enough,  or  for  a  sufficient  number  of  generations,  to  give 
any  definite  results.  It  is  to  be  noted  that  in  the  white  family  it 
was  necessary  to  outbreed  in  the  fifth  generation.  To  return  to  the 
records  of  the  family  of  colored  mice,  No.  99,  of  the  parent  genera- 
tion, made  a  very  good  record  of  eight  seconds,  while  the  male  died 
before  he  was  tested.  The  first  generation  from  this  mating  gave 
one  yellow  male  and  two  gray  females.  The  male  and  one  of  the  fe- 
males made  good  records,  while  the  other  female  gave  an  -average 
time  of  63  seconds.  The  family  average  was  40  ±  P.E.  9.0  seconds. 
The  male  of  this  generation  and  the  normal  female,  No.  102,  were 
mated  and  a  litter  of  four  males  and  three  females  resulted  that  com- 
posed the  second  generation.  All  these  mice  were  of  an  agouti  color 
in  which  a  good  deal  of  yellow  pigment  was  added.  All  the  males 
and  one  female,  No.  132,  made  good  records;  a  female,  No.  133, 
made  an  average  of  53  seconds,  and  No.  134  an  average  of  95  seconds. 
Here  the  family  average  was  31.9  ±  P.E.  8.5  seconds.  Two  matings 
were  obtained  from  the  mice  of  this  litter,  and  the  resulting  offspring 
compose  the  third  generation ;  No.  131,  with  a  very  good  average  of 
6  seconds,  was  mated  with  No.  133,  with  an  average  of  53,  and  gave 


FAMILY  HISTORIES  57 

Nos.  196  to  199  inclusive ;  while  No.  129,  average  16,  X  No.  134, 
average  95,  gave  mice  Nos.  167  to  170  inclusive.  The  litter  of  No. 
131  X  No.  133  was  composed  of  a  gray  male,  with  an  average  of  40 
seconds;  a  gray  female,  with  an  average  of  61  seconds;  a  yellow 
female  that  made  the  very  poor  record  of  134  seconds,  and  one  agouti 
female,  No.  199,  that  died  before  its  records  were  completed.  This 
agouti  female,  however,  made  very  good  records  in  the  initial  learn- 
ing, and  both  interference  periods  of  the  maze  'test  before  it  died.  Its 
records  may  be  considered  similar  to  those  of  No.  156,  already  dis- 
cussed (see  Fig.  12).  The  family  average  for  the  first  litter  in  the 
third  generation  was  78  ±  P.E.  22.4  seconds.  The  second  litter  in 
this  generation  was  composed  of  Nos.  167  to  170  inclusive ;  offspring 
of  No.  129  X  No.  134.  The  family  consisted  of  three  males  and  one 
female ;  there  was  a  yellow  male  and  a  yellow  female,  a  gray  male, 
and  finally  a  black  mouse  also  a  male.  The  two  yellow  individuals, 
Nos.  167  and  168,  made  the  poor  averages  of  81  'and  82  seconds  re- 
spectively; the  black  colored  male  took  47  seconds,  while  the  gray 
male  54  seconds.  Their  family  average  was  66  ±  P.E.  7.7  seconds. 
This  experiment  has  not  extended  far  enough  to  give  as  yet  any 
definite  results,  but  it  is  interesting  to  note,  that,  'as  was  found  in  the 
case  of  the  white  mice,  the  males  continue  to  make,  on  the  whole, 
better  average  records  than  the  females,  and  the  three  yellow  mice, 
Nos.  198,  167  and  168,  in  the  third  generation  make  the  poorest  time 
records  in  their  respective  litters.  If  there  is  a  tendency  for  the 
yellow  mice  to  be  slow  to  learn,  this  point  can  only  be  finally  deter- 
mined as  the  work  of  this  investigation  continues. 


XII.   SUMMARY 

1.  Albino  and  colored  mice  can  be  used  to  advantage  for  labora- 
tory work  in  animal  behavior. 

2.  Both  the  maze  and  the  multiple  choice  apparatus  that  were 
used  in  this  investigation  appear  well  adapted  for  this  kind  of  work. 

3.  There  is  a  (marked  difference  in  individual  behavior,  with  a 
close  correlation  between  time  and  error  records. 

4.  There  appears  to  be  a  fairly  close  relation,  in  the  maze  test  of 
this  investigation,  between  .performance  at  the  beginning  of  the  ini- 
tial learning  period  with  performance  at  the  end  of  the  same  period. 
The  quick  learners  appear  to  make  the  best  records  at  the  end  of  the 
test.     This  relation  appears  to  hold  for  the  results  in  the  multiple 
choice  test,  but  in  this  case  the  coefficient  of  correlation  is  much 
lower. 

5.  There  appears  to  be  practically  no  correlation  between  per- 
formance in  the  maze  test  with  performance  in  the  multiple  choice 
test,  and  this  may  be  due  to  factors  peculiar  to  each  test,  as  has  al- 
ready been  discussed  in  the  body  of  this  thesis. 

6.  On  the  whole,  the  animals  that  do  well  in  the  initial  learning 
period  of  the  maze  test  continue  to  make  good  time  averages  in  both 
of  the  interference  tests  and  in  the  retention  test. 

7.  The  quick  learners  appear  to  exhibit  a  considerable  amount  of 
flexibility  of  behavior. 

8.  Definite  types  of  movements  were  noted  in  the  formation  of 
habits  in  both  the  position  test  and  the  discrimination  test. 

9.  There  appears  to  be  a  certain  amount  of  interference  effect 
carried  over  from  one  type  of  reaction  to  another. 

10.  Poor  health  in  an  animal  may  not  necessarily  be  correlated 
with  slow  learning  ability,  for  when  a  habit  is  once  fixed  it  may  resist 
a  considerable  amount  of  disturbing  influence. 

11.  There  appears  to  be  no  particular  resemblance  among  indi- 
viduals of  the  same  litter,  as  judged  by  their  time  records  for  vari- 
ous tests. 

12.  There  appears  to  be  a  considerable  difference  among  different 
strains. 

13.  There  appears  to  be  a  sex  difference  in  favor  of  the  males  in 
all  the  tests  of  these  experiments. 

14.  The  females  appear  more  variable  than  the  males  in  their 
behavior. 

58 


CENTRAL  UNIVERSITY  LIBRARY 

University  of  California,  San  Diego 

DATE  DUE 


MAR  2  P  138L 

MAR    21987 

a  39 

UCSDLibr. 

001279663 


